Walk-assist devices and methods

ABSTRACT

A method for reducing an exerted energy associated with muscles acting across a joint is provided. The method including: storing energy during one or more periods of a periodic motion of the joint in which energy is absorbed by the muscles; and at least partially returning the stored energy to the muscles during one or more periods of the periodic motion in which the muscles are performing work.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to earlier filed U.S. provisionalapplication, Ser. No. 60/600,456 filed on Aug. 11, 2004, the entirecontents of which is incorporated herein by its reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to walk-assist and powergeneration devices and methods, and more particularly, to devices, whichgenerate power and/or assist movement when worn.

2. Prior Art

During walking on a flat, rigid and horizontal surface, a human subjectspends energy and tires. On the other hand, if the human subject wereinstead riding a bicycle that is in good condition, the subject has tospend a significantly less amount of energy to travel the same amount ofdistance. And in general, the faster the person walks (or runs), thedifference between the amount of energy that has to be spent to travel acertain distance on foot or on bicycle becomes greater. The reason forthis significant difference in the amount of energy that a person has tospend to travel a certain amount of distance can be described asfollows. Here, the objective is to account for the major sources ofenergy expenditure and for the secondary and generally less significantbut complex processes that demand energy expenditure during locomotion.

During normal walking (gait), there are two main sources of energyexpenditure. Firstly, due to the structure of the human body, energy isspent to sequentially accelerate and decelerate the lower limbs and to alesser degree certain other parts of the body (e.g., pumping arms) toachieve locomotion. This component of the energy spend by a personduring the process of locomotion is hereinafter called the “locomotionenergy”. This is the case even during a highly efficient mode oflocomotion along a straight path in which the trunk moves at a nearlyconstant velocity. During normal walking, the motion of the lower limbis nearly periodic. During each cycle of gait, the muscles acting on thelower limbs are responsible for both accelerating and decelerating thelimb segments. The muscles consume energy to apply the forces requiredto accelerate the limb segments and they consume energy to apply theforces required to decelerate the limb segments. In comparison, if theperson were riding a bicycle, following initial acceleration to aconstant travel velocity, the person has to provide minimal energy tothe human-bicycle system since no significant inertia has to besequentially accelerated and decelerated (neglecting the small frictionforces, aerodynamic drag, etc.).

Secondly, muscle forces have to provide the required forces across thevarious joints of the lower extremities and the back and neck to keepthe body upright (or on the seat of the bicycle) and to provide for astable posture. Thereby the person has to spend energy to provide suchmuscle forces. This component of the energy spent by a person during theprocess of locomotion is hereinafter called the “stance energy”. Theamount of energy required for this purpose is usually significantlyhigher than the required minimum since the muscle groups generally acttogether and provide opposing (isometric) forces that provide jointpreloads that in turn provide for extra stability margin.

Thus, in order to more significantly reduce the amount of energy that aperson has to spend during locomotion, the amount of aforementioned“locomotion energy” and “stance energy” that is consumed by the muscleshas to be reduced. Currently, certain devices are known in the art thatare used to reduce joint loads and/or to reduce muscle forces (mostly inthe lower extremities) that are required for stance stability. Thesedevices do reduce the “stance energy”, some a very small amount and someslightly more, and are discussed below. There is, however, no devicecurrently available for directly reducing the “locomotion energy”.

To provide or supplement muscle forces in achieving a stable stance,various assist or support devices have been developed. Such stance orsupport assist devices generally help to reduce the muscle forces thatare required to keep the body upright and to provide stance (sitting)stability. As a result, such devices also help reduce the aforementioned“stance energy” requirements during locomotion to various degrees. Aperson may use one or more of such assist or support devices due to thelack of adequate muscle force levels or control due to age, jointdisease, soft or hard tissue injury or operation, etc. These devicesinclude various braces, walkers, canes, crutches, and the like. As aresult, the forces that the muscles have to provide and the forcesacross the various joints of the lower extremities are generallyreduced. The currently available assist devices may be divided into thefollowing two categories. Here, various shoe inserts, componentsincorporated into the shoes, etc., are not considered since they areprimarily used to modify force distribution on the foot and its jointsby providing certain type of interface between the foot and the shoe(ground).

-   1. Various bracing devices used to bridge one or more joints, for    the primary purpose of reducing the load transmitted through the    joint. The level of muscle forces that act across the joint to    provide joint stability is also reduced, thereby further reducing    the joint forces. Depending on the effectiveness of the bracing in    providing joint (stance) stability, the “stance energy” is reduced    by a certain amount.-   2. Various walk assist devices such as walkers, canes, crutches,    etc., for the primary purpose of reducing load on one or both lower    extremities. When such assist devices are used, other muscles,    usually the arm and shoulder and certain upper body muscles, must    then provide the forces needed to assist stance stability and    locomotion. The person obviously has to spend energy to provide the    latter muscle forces. The currently available assist devices do not    significantly reduce the total stance energy expended but merely    transfer the load from the lower limb muscles to the muscles of the    arm and the upper body.

SUMMARY OF THE INVENTION

The present invention provides methods and devices to reduce both“locomotion energy” and the “stance energy”. Such methods have beendeveloped e.g., based on the inherent characteristics of gate and thework done by the muscle forces to affect locomotion and stancestability. Based on such methods, devices are disclosed for thefollowing exemplary applications:

-   -   1. Methods and devices to reduce “locomotion energy”. A number        of embodiments are disclosed that provide a wide rage of        locomotion energy reduction. Such devices can be simple and        totally passive to eliminate smaller portions of the locomotion        energy. More complex devices can be used to eliminate larger        portions of the locomotion energy. The complexity in the latter        devices can be in terms of the mechanisms to be used and the        active components and controls that are needed to make them        highly effective. By reducing the amount of locomotion energy        that the user has to provide during locomotion (walking and        running), the user becomes less fatigued. A user may, therefore,        use these devices for the purpose of walking while getting less        fatigued, or walking or running longer distances or with heavier        loads with essentially the same level of induced fatigue.        Embodiments with only passive elements and those with active        elements and also microprocessor-controlled versions to achieve        higher efficiency, adaptability and programmable operation are        also disclosed.    -   2. A modified version of the above methods to reduce “locomotion        energy” that allows the conversion of at least a portion of the        saved energy to electrical energy which can be stored and/or        directly used to power a device. A number of related embodiments        are also disclosed. By using the disclosed devices, a user        reduces locomotion energy, thereby gets less fatigued during        walking and/or running, while at the same time can generate        electrical energy that can be used directly or stored for later        use. Embodiments with active elements (in addition to the        electrical power generation elements and related electronics) to        achieve higher efficiency and those operated by programmable        microprocessors are also disclosed.    -   3. A modified version of the above methods to reduce both        “locomotion energy” and “stance energy”. Embodiments with only        passive elements and those with active elements, including those        operated by programmable microprocessors are also disclosed. The        latter embodiments include those with sensors for measuring a        level of stance stability and fatigue to adapt the parameters of        the active components of the device.    -   4. A modified version of the aforementioned methods to reduce        “locomotion energy” in which the phases of operation are        reversed, i.e., certain levels of accelerating forces are        provided to the limbs while the muscle forces are attempting to        decelerate them and decelerating forces are provided while the        muscle forces are attempting to accelerate the limbs. The forces        applied to oppose the action of the muscle forces help the user        exercise the affected muscles. The opposing forces are        hereinafter called “exercising forces”, the energy spent by the        user to provide their action is hereinafter called “exercise        energy”, and such devices are hereinafter “exercising devices”.        Embodiments that allow selective application of “exercising        forces” to exercise one or a group of muscles and to allow the        user to vary the level of the exercising forces are also        disclosed. Embodiments capable of providing a programmed        sequence of “exercising forces” and/or their levels for selected        group or groups of muscles are also disclosed.

Embodiments are also disclosed in which the above “exercising devices”are modified to reduce certain joint contact, ligament or muscle forces.The reductions are achieved by reducing “locomotion energy”, and/or the“stance energy”, and/or a certain muscle or muscle group forces, and/orthe forces transmitted across certain joint or joints. Such embodimentsare intended mainly for physical therapy and rehabilitation purposes byproviding means to adjust the level of muscle, ligament or joint contactforces. Embodiments capable of providing a programmable variation of theaforementioned forces are also disclosed.

Accordingly, a method for reducing an exerted energy associated withmuscles acting across a joint is provided. The method comprising:storing energy during one or more periods of a periodic motion of thejoint in which energy is absorbed by the muscles; and at least partiallyreturning the stored energy to the muscles during one or more periods ofthe periodic motion in which the muscles are performing work.

The joint can be the ankle or the knee.

The periodic motion can be walking or running.

The storing of energy can be done with a mechanical device.

The method can further comprise: sensing variations in the periodicmotion; and adjusting one or more of the energy stored and the energyreturned based on the sensing.

The method can further comprise allowing a user to adjust one or more ofthe energy stored and the energy returned.

The storing can comprises storing energy from two or more cycles of theperiodic motion and the at least partially returning can comprisereturning the stored energy at a predetermined portion of the periodicmotion.

Also provided is a device for reducing an exerted energy associated withmuscles acting across a joint. The device comprising: means for storingenergy during one or more periods of a periodic motion of the joint inwhich energy is absorbed by the muscles; and means for at leastpartially returning the stored energy to the muscles during one or moreperiods of the periodic motion in which the muscles are performing work.

The joint can be the ankle or the knee.

The periodic motion can be walking or running.

At least one of the means for storing energy and the means for at leastpartially returning the stored energy can be passive.

At least one of the means for storing energy and the means for at leastpartially returning the stored energy can be active.

Still further provided is a device for reducing a locomotion energyassociated with leg muscles acting across an ankle joint. The devicecomprising: a cuff worn on the leg; a shoe; and a mechanism operativelyconnecting the cuff and shoe for storing energy during one or moreperiods of a walking or running motion of the joint in which energy isabsorbed by the muscles and at least partially returning the storedenergy to the muscles during one or more periods of the walking orrunning motion in which the muscles are performing work.

The mechanism can comprise: a first intermediate member attached to theshoe; a second intermediate member attached to the cuff, the first andsecond intermediate parts being rotatably connected at a hinge; and aspring provided at the hinge which engages the first and secondintermediate members during the one or more periods of the walking orrunning motion of the joint in which energy is absorbed by the musclesand disengages during the one or more periods of the walking or runningmotion in which the muscles are performing work. The spring can beselected from a group consisting of a torsional spring, a compressivespring, and an elastic element.

The mechanism can comprise: a member operatively connected at one end tothe cuff; and first and second elastic elements fixed at one end to theshoe and at another end to the member such that the first and secondelastic elements are stretched during the one or more periods of thewalking or running motion of the joint in which energy is absorbed bythe muscles and are relaxed during the one or more periods of thewalking or running motion in which the muscles are performing work.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the apparatus andmethods of the present invention will become better understood withregard to the following description, appended claims, and accompanyingdrawings where:

FIG. 1 illustrates a schematic of a lateral view of a right leg.

FIGS. 2 a-2 d illustrate graphs showing measurements of average lowerextremity joints motion and the required net muscle induced torques fora 80 kg male.

FIG. 3 illustrates a schematic of a right leg, indicating the anklejoint angle θ₃ as measured from the foot to the leg.

FIGS. 4 a-4 d illustrate plots of the relative joint angle θ₃, thecorresponding joint angular velocity ω₃, the net moment of force actingon the ankle joint M_(A) and the corresponding mechanical power P_(A),respectively, during normal gait as a function of stride.

FIGS. 5 and 6 illustrate plots of the ankle joint angle θ₃ and themoment M_(A) about the ankle joint against during one stride,respectively, from the plots of FIGS. 4 a-4 d.

FIGS. 7 and 8 illustrate a plot of the ankle joint angle θ₃ versus themoment about the ankle joint M_(A).

FIG. 9 illustrates a schematic of an embodiment of a walk-assist devicefor use on an ankle.

FIGS. 10, 11 and 12 illustrate schematics of the embodiment of FIG. 9with a torsional spring, a linear spring and an elastic element,respectively.

FIG. 13 illustrates a schematic of another embodiment of a walk-assistdevice for use on an ankle.

FIG. 14 illustrates a schematic of two relatively rigid links andattached by a rotary joint.

FIG. 15 illustrates a schematic of the two links of FIG. 14 with anadded elastic (spring) element.

FIG. 16 illustrates a sliding joint having a braking element that allowsrelative displacement of two relatively rigid components.

FIG. 17 illustrates a section view of the sliding joint of FIG. 16 astaken along line 17-17 of FIG. 16.

FIG. 18 illustrates a schematic of a simple linkage mechanism.

FIG. 19 a illustrates two of the links of FIG. 18. FIG. 19 b is adiagram showing links 190 and 191 of FIG. 19 a and FIG. 19 c is adiagram showing links 191 and 192.

FIG. 20 a illustrates a schematic showing three elements connected inseries and FIG. 20 b illustrates a brake element and spring elementconnected in series.

FIG. 21 illustrates a plot of the force versus displacement for thethree elements connected in series of FIG. 20 a.

FIG. 22 illustrates an embodiment of a power generating walk-assistdevice.

FIGS. 23 a and 23 b illustrate a piezoelectric material basedpower-generating element. In FIG. 23 a, the piezo generator is attachedto the elastic element with a parallel configuration. In FIG. 23 b, thepiezo generator is attached in series to the elastic element.

FIGS. 24 a illustrates a schematic of a piezo generator. FIGS. 24 b and24 c illustrates bending elements of the piezo generator of FIG. 24 a.

FIG. 25 illustrates a schematic of the piezo generator of FIG. 24 aunder an applied pair of tensile forces.

FIG. 26 illustrates a schematic of an electric power generator and itselectrical energy collection and regulation electronics.

FIG. 27 illustrates a schematic of an elastic element and piezogenerator element assembly with a brake element positioned in parallelwith the power generator where the power generator is placed in parallelwith the elastic element.

FIG. 28 illustrates a schematic of an elastic element and piezogenerator element assembly with a brake element positioned in serieswith a power generator.

FIG. 29 illustrates a schematic of an embodiment of a device configuredto exercise muscles.

FIG. 30 illustrates a plot of moment (torque) T versus angular rotationθ for a spring element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides methods and devices to reduce “locomotionenergy” and/or “stance energy”, or obtain other novel variations asenumerated above. As it is described below, the disclosed novel methodis based on the inherent characteristics of gate and the work done bythe muscle forces to affect locomotion and stance stability. In thisdisclosure, for the sake of simplicity, this method is first describedby its application to a device for the human knee, which allows the userto reduce the component of the “locomotion energy” associated with themuscles acting across the knee joint during locomotion (walking orrunning). It is then shown how the muscle forces required for stancestability across the knee joint can also be reduced. The method isgeneral and applicable to the other joints of the subject, bothindividually and as a group. The method also applies to other linearand/or rotational motion of other segments of the body. The descriptionof the aforementioned related methods and devices and their variousembodiments are provided next.

A schematic of the lateral view of a right leg is shown in FIG. 1. Forthe sake of simplicity it is assumed that locomotion is occurring in afixed vertical plane and is represented by a simple model. The thigh 101is modeled as a link 102 connected to the trunk (not shown) and the kneeby rotary joints 103 and 104, respectively. Similarly, the lower leg 105is modeled as a link 106 connected to the knee joint 104 and an anklejoint 107. The foot is indicated by reference numeral 108 and is alsoconnected to the ankle joint 107. In this simple model, the angle θ(109) between the thigh 102 and the leg 106 is essentially between thefemur (link 102) and the tibia (link 106) in the direction shown in FIG.1, and is hereinafter referred to as the knee angle.

The torque τ (110) is the total torque produced by the muscles acting onthe knee joint 104 to produce or maintain the angle θ (109). The torqueτ (110) is hereinafter referred to as the knee torque or knee moment.

The net mechanical power P at any given point of time due to the torqueτ (110) acting at the knee joint rotating with the angular velocityV_(θ) is given by:P=τV_(θ)  (1)

In periods in which the power P, equation (1), is positive, the kneetorque and angular velocity have the same sense and the input of energyby the leg muscles into the (leg) system at the knee joint 104 ispositive. On the other hand, when the power P is negative, the legmuscles are taking energy out of the (leg) system, i.e., are absorbingenergy. In either case, the muscles spend energy, and as a result, thesubject gets fatigued. In general, if the subject is walking on ahorizontal surface, the above energy consists mostly of kinetic energy.

In any range of angular rotation, the mechanical work U done by the kneetorque τ can be found directly by integrating the product of the torqueand angular rotation over the specified range of knee motion.Alternatively, the mechanical work U over an interval of time may bedetermined by integrating the power P, equation (1), over the specifiedinterval of time as: $\begin{matrix}{U = {\int_{t_{initial}}^{t_{final}}{P{\mathbb{d}t}}}} & (2)\end{matrix}$

Consider a subject walking with a fixed cyclic gate. The kinematics anddynamics of such cyclic gates for humans have been extensively studiedand reported in the published literature, such as in Bresler, B.,Frankel, J. P., “The forces and moments in the leg during levelwalking,” Trans. ASME 72:27-36 (1950); Cappozzo, A., Leo, T., Pedotti,A., “A general computing method for the analysis of human locomotion,”J. Biomechanics, 8:307-320 (1975); Chao, E. Y., “Justification oftriaxial goniometer for the measurement of joint rotation,” J.Biomechanics, 13:989-1006 (1980); David A. Winter, The Biomechanics andMotor Control of Human Gait: Normal, Elderly and Pathological, SecondEdition, University of Waterloo Press (1991); and Winter, D. A.,Sidwall, H. G., Hobson, D. A., “Measurement and reduction of noise inkinematics of locomotion,” J. Biomechanics, 7:157-159 (1974).

For example, measurements of average lower extremity joints motion andthe required net muscle induced torques are presented in FIGS. 2 a-2 dfor an 80 kg male. The average rotation at the knee joint 104 during the“stride period” of a natural “cadence” is shown in FIG. 2 a, with theintervals in which the knee is extending (straightening) and flexing(bending) clearly indicated. “Stride Period” is defined as the timebetween two consecutive initial contacts between the right heel and theground during natural walking. “Cadence” is the number of steps per unittime. Natural Cadence is the number of steps per unit time when theperson is walking at their natural pace.

The corresponding angular velocity of the knee V_(θ) and knee torque τare also shown in FIGS. 2 b and 2 c, respectively. The correspondingpower P is shown in FIG. 2 d.

As can be seen in FIG. 2 d, there are four intervals, labeled as N1(from time t₁ to time t₂), N2 (from time t₃ to time t₄), N3 (from timet₅ to time t₆), and N4 (from time t₇ to time t₈), within which the inputpower is negative. During the intervals N1, N2, N3 and N4, the legmuscles, as a whole, are absorbing energy and the knee torque (moment)and angular velocity are in opposing directions. In the other intervalsN5 (from time t₆ to time t₁), N6 (from time t₂ to time t₇) and N7 (fromtime t₈ to time t₃), however, the muscles are doing work to mostly addto the kinetic and potential energy of the leg system. Duringlocomotion, muscle forces in a similar manner act on other lowerextremity joints (and to a lesser degree other body segments) toaccelerate and then to decelerate them during each cycle of gate (incertain cases, e.g., at the knee joint 104, several such intervals arepresent during each cycle of gait). In addition, the muscle forces alsodo work to raise certain segments of the body, for example the foot andthe leg, thereby increasing and later decreasing their potential energy.It is also noted that many muscles act on more than one joint and thatdifferent segments of the body, e.g., the lower extremities, undergo amore complex pattern of simultaneous motions.

Now consider the case in which the energy to be absorbed during theintervals N1, N2, N3 and N4 is stored in certain mechanical (orelectrical) storage devices and partially or wholly returned to the legsystem during the N5, N6 and N7 intervals to partially or whollyeliminate the need for the leg muscles to input the required energyduring the latter intervals. In a similar manner, the energy absorbed bythe muscle forces acting across other joints such as ankle and the hipjoints may be stored (as electrical energy and/or mechanical energy) andreturned to the leg system when the muscle forces are required toprovide energy to the affected body segments.

Such a device is a walk-assist device that significantly reduces theamount of work that the leg muscles have to do during walking orrunning, i.e., it would significantly reduce the aforementioned“locomotion energy”. As a result, the walk-assist device significantlyreduces the amount of work that the leg muscles have to do duringwalking or running.

In fact, if a subject is walking on a horizontal surface and if frictionlosses at the joints, friction losses between the shoes and the ground,aerodynamic drag on the body, etc., are neglected, it is theoreticallypossible to totally eliminate the aforementioned “locomotion energy”.This can be done using the aforementioned method to construct awalk-assist device that operates simultaneously across all the joints ofthe lower extremities, storing e.g., mechanical energy that the muscleshave to provide to absorb kinetic and/or potential energy from the limbsand providing the stored mechanical energy to the limbs when they needto increase their kinetic and/or potential energy. Such a system canoperate across all the joints of the lower extremities. The subjectusing such a device need only provide “stance energy” and energy toovercome dissipation of energy due to friction, aerodynamic drag, etc.,similar to when the subject rides a bicycle on a flat horizontalsurface.

In general, and is shown in FIG. 2 d, the input work by the leg musclesas a function of angular rotation of the knee and therefore time has acomplex profile. Thus, the resulting walk-assist devices can requiremechanisms with mechanical elements such as brakes and clutches andsensors and control units to allow the device to take full advantage ofthe available energy during different intervals of the locomotion.However, totally passive devices that would eliminate at least part ofthe work that the leg muscles have to do during walking or running arealso possible. The subject using such a walk-assist device can then walkwhile spending less energy, thereby getting less tired. Alternatively,the subject can walk longer distances or for longer periods of timeswithout getting more tired than he/she would for a shorter distancewithout the present device. In addition, as it is shown later in thisdisclosure, simple modification of such walk-assist devices would allowthem to also support the static and dynamic loads due to the weight ofthe user and the load that is being carried by the user. As a result,the “stance energy” that the user has to spend is also significantlyreduced. Such a walk-assist device would then allow the user to walkwhile spending even less energy, or to walk longer distances and/or tocarry heavier loads.

Methods and Devices to Reduce “Locomotion Energy”

The application of the aforementioned basic method to the development ofwalk-assist devices for the ankle joint to reduce the “locomotionenergy” is now described. The method is, however, general and applicableto other joints of the lower extremity and to walk-assist devicesextending across more than one joint. The method also applies to otherperiodic linear and/or rotational motion of other segments of the bodyduring walking and/or running. For such periodic linear and/orrotational motions, devices that operate in a manner similar to thosefor the lower extremity joints can be constructed to reduce the amountof mechanical energy that the related muscles have to provide duringwalking or running.

FIG. 3 shows the schematics of a right leg, indicating the ankle jointangle θ₃ (121), as measured from the foot to the leg. The plots of therelative joint angle θ₃ (121), the corresponding joint angular velocityω₃, the net moment of force acting on the ankle joint M_(A) and thecorresponding mechanical power P_(A) during normal gait as a function ofthe stride can be obtained from the known methods of the prior art andare shown in FIGS. 4 a-4 d, respectively. The stride begins at heelcontact, HC, and continues until the next consecutive heel contact ofthe same foot. Toe off, TO, occurs after about 0.64 of the stride and isindicated by the dashed vertical line. The first 0.64 of the striderepresents a stance phase for the leg, while the remainder of the striderepresents a swing phase.

As can be seen in the plot of the mechanical power P_(A) in FIG. 4 d,following the heel contact (point HC), the mechanical power assumes anegative value starting from around the point A and remains negativeuntil the point B (the region between the points A and B are shownbounded between two solid vertical lines). In this region, themechanical power is negative, i.e. the moment of force and angularvelocity have opposite directions. During this interval, the angularvelocity ω₃ is always positive (FIG. 4 b), indicating that the foot isrotating counterclockwise with respect to the shank. Since the foot isin contact with the ground, one can also picture the foot as being fixedflat on the ground and the shank rotating clockwise relative to thefoot. The moment M_(A) (FIG. 4 c) about the ankle joint is negativeduring this portion of the stride; therefore it has a clockwisedirection. Now if the foot is considered to be fixed, the moment M_(A)is then seen to be acting in a counterclockwise direction, therebymaking the mechanical power P_(A) negative, which means that during thisperiod, the muscles acting on the ankle joint are absorbing energy.

In FIGS. 5 and 6, the plots of the ankle joint angle θ₃ (121) and themoment M_(A) about the ankle joint against during one stride are shownagain from the plots of FIGS. 4 a-4 d. In FIG. 6, the point A at whichthe moment M_(A) is shown.

From the joint angle θ₃ (121) and the moment M_(A) about the ankle jointduring one stride, FIGS. 5 and 6, the moment M_(A) can be plottedagainst the ankle joint angle θ₃ (121), as shown in FIG. 7. The points Aand B (where the mechanical power P_(A) is zero), the toe off TO andheal contact HC are marked. If the curve is traversed from the point ofheel contact to point A, we find that point A occurs when the momentM_(A) is zero, thereby making the mechanical power P_(A) zero.Continuing downward and in the direction of Arrow 122 we reach the pointB. We find that point B is located at an extreme angular position,corresponding to a zero value of angular velocity, thereby again makingthe mechanical power P_(A) zero. In the region between the points A andB the mechanical power is negative, i.e., the muscles acting on theankle joint are absorbing energy of the leg system, thereby tending toreduce the total kinetic and potential energy of the leg. On the otherhand, in the region between B and toe off TO, the mechanical power ispositive, i.e., the muscles acting on the ankle joint are adding energyto the leg system, thereby tending to reduce the total kinetic andpotential energy of the leg.

It can also be observed from FIG. 7 that the area between the curve fromthe point A to B along the arrow 122 and the zero moment (M_(A)) line isthe work that the leg muscles have to do to absorb the kinetic andpotential energy of the leg during the corresponding portion of thestride. On the other hand, the area under the curve from the point B tonear the TO and the zero moment (M_(A)) line is the work that the legmuscles have to do to add kinetic and/or potential energy to the legsystem during the corresponding portion of the stride. Therefore, theamount of energy that is to be absorbed by the leg muscles is smallerthan the amount of the energy to be provided by the leg muscles.Neglecting the energy lost to friction, aerodynamic drag, etc., and alsoassuming that the trunk is moving at a constant speed, then the extrainput energy is mostly to increase the kinetic and/or potential energyof the other segments of the lower limb and/or absorb the same. Inactual walking, some energy is actually lost, and a certain amount ofenergy is transferred to the trunk to allow for its translational androtational “oscillations”, which similar to the leg, require input andoutput (energy absorption) from the body muscles.

The ankle joint angle θ₃ (121) versus the moment about the ankle jointM_(A) is shown again in FIG. 8. In FIG. 8, the point P5 corresponds tothe moment of heel contact (HC in FIGS. 4-6 ), following which the anklejoint angle θ₃ versus ankle joint moment M_(A) goes through the pointsP6 through P17. The area under the above curve from the point P6 to thepoint P9 and the zero moment (M_(A)) line is the aforementioned work(hereinafter referred to as W_(ab)) that the leg muscles have to do toabsorb the kinetic and potential energy of the leg during thecorresponding portion of the stride. The area under the above curve fromthe point P9 to the point P15 and the zero moment (M_(A)) line is theaforementioned work (hereinafter referred to as W_(add)) that the legmuscles have to do to add kinetic and/or potential energy to the legsystem during the corresponding portion of the stride.

As can be clearly observed in FIG. 8, the work W_(add) is significantlygreater than the work W_(ab). This means that for the case of the ankle,a passive (no input energy device such as a motor) walk-assist devicethat is to store the absorbed work W_(ab) and pass it back to the legthrough the ankle joint to reduce the work W_(add) by the same amount(here, we are assuming an ideal system for the sake of describing thepresent method and related devices) is limited to a total energyexchange level of W_(ab). Such a device can have a spring element with a(non-linear) spring rate k_(M), given byM_(A)=k_(M) θ₃   (3)

The ideal spring rate would yield an ankle joint moment M_(A) versusankle joint angle θ₃ that traces the curve from the point P6 to thepoint P9 and back as the ankle joint θ₃ is varied in the correspondingrange of ankle joint angles shown in FIG. 8.

A schematic of one embodiment is shown in FIG. 9. The walk-assist device130 comprises two parts, one of which is a cuff 132 that is worn,preferably relatively tightly, on the leg 105. A second part 131 is wornon the foot, also preferably relatively tightly, and covers part orpreferably the entire foot as a shoe or a boot.

The two parts 131 and the 132 are hinged at the ankle joint by the hinge135, which maybe provided through intermediate elements 133 and 134,which are fixed to the leg part 132 and foot part 131, respectively, byany means known in the art. A torsional (linear, etc.) spring 136 (notshown in this schematic for clarity, shown in FIG. 10) is provided atthe joint 135 and provides the aforementioned non-linear ankle jointmoment M_(A) versus ankle joint angle θ₃ curve characteristic.

As can be seen in FIG. 8, the walk assist device 130 generates theaforementioned ankle joint moment M_(A) versus ankle joint angle θ₃ fromthe point P6 to P9, and zero ankle joint moment M_(A) in the remainderrange of ankle joint angle θ₃, i.e., from the point P9 to P15. Here, thesmall zero moment range from the point P5 (P17) to the point P6 isneglected, but such multi-tracked ranges of joint motion are addressedbelow. The aforementioned zero ankle joint moment M_(A) in one part andnonzero moment M_(A) in another part of the range of ankle joint angleθ₃ (without multi-tracked ranges) can be achieved using a variety ofmethods, including the following (in the following schematics, only thehinge joint 135 and its intermediate elements, i.e., the relativelyrigid elements 133 and 134 and in certain cases the leg and foot wornparts 132 and 131 are shown).

During the ankle rotation, the spring element 136 (either torsional,linear, etc.) engages the connecting parts 133 and 134 in the range thatmoment is to be generated and disengages in the remaining (zero moment)range of ankle motion. The schematic of this embodiment with torsionaland linear springs are shown in FIGS. 10 and 11, respectively. Othertypes of springs may be employed in a similar manner. In FIG. 10, thelink 133 is free to rotate relative to link 134 about the rotary joint135 without generating resistance to rotation by the torsional spring136 (a torsional springs can make a significantly larger arc, and mayeven make several turns, however, a short arc is shown in FIG. 10 forclarity), unless it enters the range 137 (starting from the position 138to the link 134 ). A similar embodiment is shown in FIG. 11, in which acompressive linear spring 143 is used to connect the link 134 to a thirdlink 141. The link 133 is free to rotate until it reaches an extension142 of link 141, at which time, the spring 143 begins to provideresistance to further rotation of the link 133 within the range 144. Inthe embodiments of FIGS. 10 and 11, the link 133 is considered to beprevented by the link 134 to rotate counter clockwise past the link 134.It is appreciated by those skilled in the art that other types ofsprings (e.g., tensile helical springs, or those working in bending andeven the structural flexibility of the two links 133 and 134 ) and otherjoints, such as living rotary joints, and linkage configurations couldbe used to perform the aforementioned tasks.

An elastic element 145 such as a natural or synthetic elastomer can alsobe attached to the links 133 and 134 as shown in FIG. 12. The link 133is free to rotate relative to the link 134 from close to the link 134 inthe counter clockwise direction until it reaches the position 146, atwhich time the elastic element 145 becomes taut (position 147), andbegins to deform elastically with further counter clockwise rotation ofthe link 133 relative to the link 134, thereby generating a restoringmoment. The links 133 and 134 and the elastic element 145 can beintegral, and are attached directly to the foot and leg worn components132 and 131, respectively. In one embodiment, the links 133 and 134, theelastic element 145 and the leg and foot components 132 and 131 areintegral and in the form of a shoe with leg brace or preferably as aboot.

In the above embodiments, the spring rate may be constant or anon-linear function of displacement (FIGS. 11 and 12) or angularrotation (FIG. 10). If the torsional spring 136, FIG. 10, has a constantrate, then the corresponding ankle joint moment M_(A) versus ankle jointangle θ₃ becomes linear and similar to the line 150 shown in FIG. 8. Theslope of the line 150 indicates the spring rate and for the one shown inFIG. 8 it is chosen to cover the entire aforementioned range ofrotation, i.e., the range corresponding to the range of points P6 to P9with minimal amount of moment above the indicated curve. The spring rateis also selected such that the moment-rotation line 150 covers as muchof the area under the curve between the points P6 and P9, i.e., to storeas much energy as possible when using a linear spring. In addition, themoment-rotation line begins from zero moment, indicating that thetorsional spring 136 is not preloaded, which in certain cases canincrease the total amount of energy that could be stored in the springelement.

If the spring element 143 in the joint mechanism shown in FIG. 11 has anear constant spring rate and if the range of rotation 144 is relativelysmall (such as about 12 deg. as seen in FIG. 8 for the ankle joint),then the resulting ankle joint moment M_(A) versus ankle joint angle θ₃relationship becomes nearly linear. For larger ranges of angularrotation, the above relationship becomes a function of the angle 144(FIG. 11).

In the three embodiments shown in FIGS. 10-12, the spring rate may beselected not to be constant. An advantage of using non-linear springs isthat the spring force (moment) versus displacement (rotation)characteristics maybe selected such that the resulting ankle jointmoment M_(A) versus ankle joint angle θ₃ curves become close to thecurve from the point P6 to P9, FIG. 8. As an example, the curve 151shown in FIG. 8 results in the storage of most of the energy availableduring the ankle rotation from P6 to P9 and can be readily produced byan elastomeric element used in the embodiment of FIG. 12. In addition,by using springs with appropriate non-linear force (moment) versusdisplacement (rotation) characteristics, the embodiments of FIGS. 11 and10 may produce ankle joint moment M_(A) versus ankle joint angle θ₃curves that are very close to that of curve 151 in FIG. 8.

Furthermore, instead of using non-linear spring (elastic) elements, onemay use linkage mechanisms (preferably made with living joints) or camsto achieve the desired force (moment) versus displacement (rotation)characteristics. The corresponding devices may, however, become morecomplex and are not the preferred choice whenever simple spring orelastic elements could suffice, even though more complex force (moment)versus displacement (rotation) characteristics could be obtained usingcams and more complex mechanisms.

In the embodiment shown in FIG. 9, the ankle joint is shown asessentially fixed relative to the foot and the leg. However, the actualinstantaneous axis of rotation of the ankle (and the knee) joints isneither fixed nor always perpendicular to the plane of locomotion. As aresult, it is highly preferable to provide embodiments in which theinstantaneous axis of rotation is allowed to float and tilt in order tofollow the actual unconstrained axis of rotation as closely as possible.In practice, since the axes of joint rotations undergo relatively smalldisplacements and tilting angles, therefore, they require minimal rangeof displacement and tilting freedom. The axes of joint rotations isdiscussed in e.g., Rastegar, J., Miller, N., and Barmada, R., “AnApparatus for Measuring the Load-Displacement and Load-DependentKinematic Characteristics of Articulating Joints. Application to theHuman Ankle Joint,” ASME Journal of Biomechanical Engineering 102, pp.208-213 (1980); Rastegar, J., Piziali, R., L., Nagel, D. A., andSchurman, D. J., “Effect of Fixed Axis of Rotation on the Varus-Valgusand Torsional Load-Displacement Characteristics of the In-Vitro HumanKnee,” ASME Journal of Biomechanical Engineering 101 (1979); Piziali, R.L., Rastegar, J., and Nagel, D. A., “The Contribution of the CruciateLigaments to the Load-Displacement Characteristics of the Human Knee,”ASME Journal of Biomechanical Engineering 102, pp. 277-283 (1980);Piziali, R. L., Rastegar, J., and Nagel, D. A., “Measurement of theNon-Linear, Coupled Stiffness Characteristics of the Human Knee,”Journal of Biomechanics 10, (1977); Rastegar, J., Miller, N., andBarmada, R., “Relative Motion of the Tibia With Respect to the FootDuring Internal-External Rotation of a Human Ankle Joint,” ASME PaperNo. 79-Bio-4; Rastegar, J., Miller, N., and Barmada, R., “Measurement ofthe Internal-External Load-Displacement Characteristics of the In-VitroHuman Ankle Joint,” ASME Paper No. 79-Bio-3; Miller, N., Rastegar, J.,and Barmada, R., “Torsional Characteristics of the Human Knee and itsPassive Elements Under Simulated Anatomical Conditions,” ASME AdvancesIn Bioengineering, pp. 91-93 (1979); Rastegar, J., Miller, N., andBarmada, R., “Relative Motion of the Tibia With Respect to the FootDuring Internal-External Rotation of a Human Ankle Joint,” ASME SummerConference (1979); Miller, N., Rastegar, J., and Barmada, R.,“Internal-External Load-Displacement Characteristics of the In-VitroHuman Ankle Joint,” ASME Summer Conference (1979); Piziali, R. L.,Rastegar, J., and Nagel, D. A., “The Axis of Varus-Valgus Rotation ofthe In-Vitro Human Knee Joint,” Proceedings of 24^(th) OrthopaedicResearch Society (1978); Rastegar, J., Piziali, R. L., and Nagel, D. A.,“Varus-Valgus Stiffness of the In-Vitro Human Knee Joint,” Proceedingsof 23^(rd) Orthopaedic Research Society (1977); Rastegar, J., Piziali,R. L., and Nagel, D. A., “Torsional Load-Displacement Characteristics ofthe In-Vitro Human Knee,” Proceedings of 30^(th) ACEMB (1977); Piziali,R. L., Rastegar, J., Nagel, D. A., and Hight, T., “Knee Mechanics andAnalytical Modeling in Lower Limb Injuries,” Proceedings of 2^(nd)International Conference on Ski Trauma and Ski Safety, Spain (1977);Rastegar, J., Piziali, R. L., and Nagel, D. A., “Varus-Valgus Stiffnessof the In-Vitro Human Knee,” ASME Winter Annual Meeting (1976); andRastegar, J., Piziali, R. L., Seering, W. P., and Nagel, D. A., “TheFunction of the Passive Knee Structures in Anterior-Posterior TibialDisplacement,” Proceedings of 28^(th) ACEMB (1975).

In the embodiment of FIG. 13, the walk-assist device 160 for the anklejoint consists of the aforementioned leg cuff 132 and foot worn part 131(preferably shoe or boot, hereinafter referred to as shoe 131) elements.A relatively flat element 161 is fixed to the leg cuff 132. The element161 is relatively thin but rigid in bending in its own plane, i.e., inthe plane of the illustration, but is relatively flexible in bending outof the plane of the illustration. Two elastic elements 162 and 163 arefixed to the shoe 131 on one side (162 a, 163 a) and fixed to theelement 161 on the other side (162 b, 163 b) as shown in FIG. 13. Thus,as the leg 105 rotates clockwise relative to the foot, the two elasticelements 162 and 163 are stretched, thereby generating a couple (moment)about a center of rotation 164. One advantage of this embodiment is thatthe two elastic elements 162 and 163 provide a moment about the centerof rotation 164 and generate minimal joint forces. This embodiment maybe modified by not fixing the element 161 to the leg cuff 132, butconstraining it loosely within a pocket (not shown) so that it is freeto displace laterally within a certain range of leg rotation relative tothe foot and force relative rotation of the element 161 relative to thefoot in another range of such rotation to obtain ankle joint momentM_(A) versus ankle joint angle θ₃ curves close to the curve from pointP6 to P9 shown in FIG. 8. This modification has also an advantage ofallowing the instantaneous center of rotation 164 (together with theelement 161) to displace laterally to near the actual instantaneouscenter of rotation since the elastic elements 162 and 163 have minimalresistance to lateral bending. Similarly, since the element 161 and theelastic elements 162 and 163 have minimal resistance to bending andtorsion in and out of the plane of illustration, the instantaneous axisof rotation (normally perpendicular to the plane of illustration) can betilted up and down and/or to the right and left a small amount toclosely follow the actual instantaneous axis of ankle rotation. Inaddition, since the center of rotation 164 is located central to theelastic elements 162 and 163, the center of rotation 164 may be floatedup along the stem 165 of the element 161 or below the stem 165 whileminimally affecting the nearly pure couple nature of the forcesgenerated in the elastic elements 162 and 163.

In general, other coupling elements that allow relatively freedisplacement of the axis of rotation of the ankle joint and its slighttilting could be used together with preferably couple producing elasticelements or torsional springs to provide the aforementioned joint momentversus angular rotation. Such couplings are well known in the art andare used regularly to couple shafts such that they can toleraterelatively small offsets and angular misalignment. Such couplings are,however, generally bulky and occupy a considerable space, which is notdesirable for the present applications. Therefore embodiments such asthe one shown in FIG. 13 are more appropriate and could be made as acompact device that could readily be integrated into boots or as alightweight bracing. The best mechanism design for the aforementionedpurpose is one that operates such that the loads applied to the passiveankle joint elements such as ligaments and the joint surface contactsare minimally altered or reduced and not increased.

It should be noted that in the schematics of FIGS. 9 and 13, only onelateral joint mechanism for energy storage and release is shown. Ingeneral, however, the preferred embodiments use one such mechanism onboth sides of the ankle (and the knee) joint to provide a more uniformand symmetric moment across the joint.

In the above embodiments, the portion of the ankle joint moment M_(A)versus ankle joint angle θ₃ curve from point P6 to point P5 (P17) wasneglected and the aforementioned embodiments would produce the curves150 or 155 without the segment corresponding to the segment P6 to P5(P17). If it is desired to keep the segment P6 to P5 (P17) with samepassive mechanisms, then the mechanisms shown in FIGS. 9-13 and theothers described above must only produce the portion of the ankle jointmoment M_(A) versus ankle joint angle θ₃ curve positioned to the rightof the vertical line 166, FIG. 8, to the point P9. For example, thespring (elastic) elements that produce the 150 and 151 curves can stillbe used, but for the aforementioned range, i.e., from the vertical line166 to the point P9. The corresponding spring (elastic) elements must,however, be preloaded to the line 167, FIG. 8, using a number of methodsknown in the art, e.g., by providing a stop to prevent a preloadedspring or elastic element from moving back to its no-load configuration.

From FIG. 8, the amount of energy to that the muscles have to spend toabsorb the leg kinetic and or potential energy, i.e., approximately thearea under the curve to the zero moment line from the point P6 to P9 maybe estimated by simply counting the number of grid squares, in this caseabout 5.1 squares. From the units in FIG. 8, it is readily seen thateach square corresponds to 20 N-m times 5 degrees or about 1.75 N-m orJoules of energy. The energy that the muscles have to spend to addkinetic and or potential energy to the leg system, i.e., approximatelythe area under the curve to the zero moment line from the point P9 toP15 may be similarly estimated to be 15 squares. Thus, the total energythat the muscles have to provide about the ankle joint is about 20.1squares, i.e., 20.1×1.75=35.175 J. With the aforementioned embodimentsusing an elastic element with the spring rate 151, FIG. 8, 5.1 squares,i.e., 5.1×1.75=8.925 J of energy is stored in the elastic element whilewalk-assist device is absorbing kinetic and/or potential energy from theleg system (from the point P5 to P9, FIG. 8) and would provide it backto the leg system during the portion of the stride that kinetic and/orpotential energy has to be increased (from the point P9 to P15, FIG. 8).Thus, up to 2×8.935=17.85 J out of the above 35.175 J, or up to 50.7percent of energy spent by the muscles forces at the ankle joints couldbe saved by using the disclosed walk-assist devices. In practice,however, due to friction losses and other inefficiencies, the actualenergy savings should be expected to be lower, but as can be seen, issignificant nonetheless.

In addition, as shown below, the total savings in the energy spent bythe muscles acting at the ankle joints can be significantly increased byproviding a walk-assist device that operates as a total leg system onall the joints of the lower extremity. For the case of the ankle joint,such a device would store energy that has to be absorbed by the musclesacting at the other joints of the leg and transfer the energy to theankle joints during the ankle joint rotation from the point P9 to P15,FIG. 8.

With passive elastic (spring) elements, whether with linear ornon-linear load (force, moment, torque, etc.) versus displacement(linear displacement, bending displacement, rotation, etc.)characteristics, hereinafter referred to as simply the load-displacementcharacteristics, it is impossible to obtain complex rate characteristicsthat are required to follow the type characteristics shown for the anklejoint in FIG. 8. As can be seen in FIG. 8, during the stride, the anklejoint moment versus ankle joint rotation curve starts from the point P5;becomes slightly positive as the angle is reduced, then comes back tozero at the point P6; then reverses its slope providing increasinglevels of moment (negative in sign) with increasing angle θ₃ up toaround the point P9; then as the ankle joint angle decreased, it followsthe branch from the point P9 through P10-P14, ending up at the pointP15, this time at higher (more negative) moment levels for correspondingangles (within the range of P5 to P9); the ankle joint is then returnedto the starting point P5 (indicated also as P17 in FIG. 8), at near zeromoment levels following the line from the point P15 through P16 to thepoint P17.

Another characteristic of the load-displacement characteristics of thetype shown for the ankle joint in FIG. 8 (similar types ofload-displacement characteristics during gate are found at the knee andthe hip joints) is that the total amount of the energy that is absorbedby the muscles (effectively the area under the curve from the point P6to the point P9 and the zero moment line) is not the same as the amountof the energy that the muscles have to provide to increase the kineticand/or potential energy of the system (effectively the area under thecurve from the point P9 to the point P15 and the zero moment line). Inthis case, more energy is provided by the muscles through the anklejoint then is absorbed. As a result, to provide part or all the extraneeded energy from the energy stored from walk-assist device componentsmounted on the other joints of the body such as the knee and the hipjoints, the ankle joint device must be coupled (preferably) mechanicallyto the devices at those joints. Such coupling is possible but is verydifficult to accomplish without the use of any active elements. Here, byactive elements it is meant powered elements, such as those that arepowered electrically, pneumatically or by fluid power and withoutregards to the source of power, whether internally or externallygenerated. The use of purely passive elements for this task is made moredifficult considering the fact that the subject wearing the walk-assistdevice may use various gate patterns, therefore requiring the parametersof the walk-assist device to be capable of adapting to varying gatepatterns.

It must, however, be noted that with pure passive elements, as it wasshown above for the case of the ankle joint, walk-assist devices canstill significantly reduce the amount of energy that the muscles have toprovide during locomotion. However, to increase their efficiency evenmore and to expand the application of such devices to several otherfields as described below, some or all the aforementioned shortcomingsof purely passive constructions can be overcome. In the following, anumber of embodiments that use very simple and low power active elementsare disclosed that can be used to construct walk-assist devices withoutthe aforementioned shortcomings.

The basic active element of the aforementioned embodiments is a braking(or locking) element. Such braking elements are used to stop linear orrotary motions of relatively rigid parts, and for this reason may bemore appropriate to call them locking elements. Such braking elementsmay in certain case also act as a clutch. In the present disclosurethese elements are generally referred to as braking elements. The mainpurpose of using such brake elements is to at times “lock” an extended(compressed) spring in place, thereby preventing it from applying apulling (pushing) force (similarly for torsional or other types ofsprings) to the components that the spring is attached to; or at timeslock two or more relatively rigid parts together, thereby preventingtheir relative motion; or at times unlock the aforementioned extended(compressed) spring, allowing it to exert pulling (pushing) force to thecomponents that the spring is attached to; or at times unlock and allowthe relative motion of aforementioned two or more relatively rigidparts. The aforementioned relative motions may be translational orrotational or may be a combination of the two.

In FIG. 14, two relatively rigid links 170 and 171 are shown attached bya rotary joint 172. The two links are free to rotate relative to eachother, thereby varying the angle 173. By positioning a braking element(not shown) at the joint 172, the links 170 and 171 can be lockedtogether, thereby forming a relatively rigid structure at any desiredangle 173.

In the schematic of FIG. 15, the two links 170 and 171 shown in FIG. 14are shown with an added elastic (spring) element 174. The aforementionedbraking element (not shown) is still considered to be present at orabout the joint 172. At any point in time and while the elastic element174 is in tension or compression, if the braking element locks the joint172, i.e., prevents the relative motion between the two links 170 and171, then the two links 170 and 171 would form a structure and thepotential energy stored in the elastic element 174 becomes an internalenergy to the resulting structure, and potential energy could no longerbe transferred to the spring element through the links or from thespring element to the links.

It is appreciated by those skilled in the art that even though in theembodiment of FIG. 15 a helical spring 174 is shown with the rotaryjoint 172, similar braking elements may be used to lock and laterrelease relative motion between two or more elements joined with othertypes of joints and with more than one degree-of-freedom (which is thecase for the rotary joint 172), and lock in and later release potentialenergy stored in any type of elastic element, even those provided by theflexibility of the structure of the related devices. For example, asliding, planar, cylindrical or spherical joint may have been usedinstead of the rotary joint 172; or torsional, bending type orelastomeric elements may have been used in place of the helical spring174.

The braking aforementioned element may be of any type known in the art,such as a magnetic or brake shoe type operated electrically,pneumatically or hydraulically that locks either the two links togetheror directly locks the joint 172. Such braking devices usually rely onfriction-generated force (moment or torque) to provide theaforementioned braking (locking) force (moment or torque). A typicalsuch braking element is shown in the schematics of FIGS. 16 and 17. Asliding joint that allows their relative displacement in the direction186 connects the two relatively rigid components 180 and 181 as shown inFIG. 16. A cross-section of the sliding joint is shown in FIG. 17. Theinner component 181 is seen to be free to move relative to the outercomponent 180 in the axial direction, i.e., in the direction indicatedby Arrow 186 (the clearance between the two components is exaggeratedfor the sake of clarity). The inner component 181 is provided with arecess with sides 187 to allow for the mounting of at least one brakingelement. The braking element consists of at least one braking pad 183and a displacement actuator 184, which imparts back and forth motion tothe braking pad 183. The actuation device may be electrically operatedsuch as like a solenoid, or may be pneumatically or hydraulicallyoperated, or operated by a piezoelectric actuation device, or any othertype of actuation device known in the art. To lock the sliding joint,the actuator 184 is activated and used to press the braking pad 183against the surface 185 of the inner component 181. As a result, thesliding motion of the inner component 181 relative to the outercomponent 180 is no longer possible. The amount of force applied by theactuator 184 and the friction coefficient between the braking pad 183and the surface 185 of the inner component 181 determines how much axialforce in the direction 186 this braking element(s) can resist beforeslippage. Such braking elements can therefore provide a limit on theamount of force (moment or torque) that the joint must resist beforeallowing slippage. This characteristic of these embodiments may be used,for example, to limit the amount of potential energy to be stored inelastic elements or the maximum force (moment or torque) that a lockedjoint should resist.

The aforementioned braking elements may be normally open, i.e., apply nobraking force without an input actuator force (moment or torque), or maybe normally closed, i.e., the applied force (moment or torque) is usedto disengage the braking element. In general, either type of brakingelement may be used in the walk-assist devices. However, it ispreferable that appropriate types be used so that in the case of loss ofactuation power, the walk-assist device does not hinder walking(running) in any way or provide a destabilizing joint force, or increasethe probability of injury or become unsafe.

Other embodiments of braking elements that are particularly suitable forthe disclosed walk-assist devices are described below.

Using an appropriate number of the aforementioned braking elements andelastic elements with linear and/or non-linear spring rates and togetherwith relatively rigid links and joints, assemblies withload-displacement characteristics that approximate that of almost any ofthe lower extremity joints, such as that of the ankle joint shown inFIG. 7, may be obtained. The braking elements, elastic elements andlinks may be configured in parallel and/or in series. Here, the load isintended to also mean moment or torque, and displacement is intended toalso mean angular displacement.

As an example, consider the schematic of the simple linkage mechanism200 shown in FIG. 18. The mechanism consists of relatively rigid links190, 191 and 193. The links 191 and 192 and the links 192 and 193 areconnected by sliding joints (not shown) that allow each pair of links toundergo a sliding motion in the direction of Arrow 198. The link 190 atits end 193 and the link 192 at its end 194 are attached to two objectsthat can undergo relative motion. For example, the mechanism 200 mayreplace the spring element 174 in FIG. 15 (in this application, themechanism 200 has to be attached to the links 170 and 171 by rotaryjoints) to provide a combination of free rotation, rigid constraint orspring element between the links 170 and 171. The mechanism 200 providessuch flexibility as follows.

Braking elements 196 and 197 similar to those described above areprovided between the links 190 and 191 and the links 191 and 192,respectively. When activated, the brake element 196 (197) locks the twolinks 190 and 191 (191 and 192) together, thereby preventing theirrelative displacement. In this configuration, the links 190 and 191 (191and 192) form a relatively rigid structure. When the brake element 196(197) is deactivated, the links 190 and 191 (191 and 192) are free toundergo relative sliding motion in direction 198. For the case of thepair of links 190 and 191, the two links are connected by the springelement 195, which when the braking element is deactivated, wouldprovide a force resisting the relative displacement of the two links,and could be used to store potential energy or to extract the storedpotential energy at the desired range of motion, and in other ranges ofmotion to either make the mechanism 200 act as a structure or allow freemotion between the connected objects in the direction of mechanism 200displacement. It is noted that in the mechanism 200, once the springelement 195 is deformed (in tension or in compression), a correspondingamount of potential energy is stored in the elastic element. All or partof this potential energy may, however, be released by disengaging thebrake elements 196 and 197, and thereby allowing the link 191 todisplace, in which case an energy dissipative element such as a frictionpad or a viscous or viscoelastic damping element is preferably used toattach either or both of the link pairs 190 and 191 and/or 191 and 192in order to minimize vibration of the released link 191.

In a modification of this embodiment, a second spring element (notshown), preferably with a spring rate different from that of springelement 195, is used to attach the links 191 and 192. As a result, bysequentially locking each spring element, the mechanism 200 is used toprovide an effective spring with three possible spring rates The firstspring rate (the spring rate of the spring element 195) is obtained bythe activation of the brake element 197 and deactivation of the brakingelement 196. The second spring rate (the spring rate of theaforementioned spring attached to the links 191 and 192 ) is obtained bythe activation of the brake element 196 and deactivation of the brakeelement 197. The third spring rate (the spring rate being equal to theinverse of the sum of the inverses of the above two spring rates) isobtained by the deactivation of both of the brake elements 196 and 197.

For the sake of simplicity, the links 190 and 191 and the spring 195 andbrake element 196 of the mechanism 200, FIG. 18 and also redrawn in FIG.19 a, are shown in the simple diagram of FIG. 19 b and marked as theassembly 210. Similarly, the links 191 and 192 and the brake element 197are shown as the schematic of FIG. 19 c and marked as the assembly 211.Two or more elements 210 and 211 may then be connected in series, inparallel or their combination to obtain almost any desired force (momentor torque) versus displacement (rotation) characteristics, such as theone shown in FIG. 7.

For example, consider the schematic of FIG. 20 a showing three elements210 (indicated as 210 a, 210 b and 210 c) being connected in series toobtain the assembly 220. In FIG. 20 a, the displacements Δx₁, Δx₂ andΔx₃ are associated with the elements 210 a, 210 b and 210 c,respectively. Let all three springs elements 195 a, 195 b, 195 c of theelements 210 have a spring rate k. If the three brake elements 196 a,196 b, 196 c are activated, then the assembly acts as a structure.However, if all the three brake elements are deactivated, the effectivespring rate K_(e) is then given by1/K _(e)=3/k or K _(e) =k/3   (4)

Now consider the situation in which the three springs elements 195 a,195 b, 195 c are at their undeformed lengths. One end of the assembly220 is fixed to the ground 201 and the end 207 is pulled by applying aforce F in the indicated direction. Initially, all the three brakeelements 196 a, 196 b, 196 c are considered to be deactivated, while theend 207 is displaced an amount X (from the point 202 to 203) as shown inthe plot of FIG. 21. During this period, the equivalent spring rate hasthe lowest value as given above, i.e., K_(e)=k/3, and theforce-displacement plot is linear (all three springs are considered tohave constant spring rates k) as shown in the plot of FIG. 21. From thepoint 203 to the point 204, one of the three brake elements isactivated, thereby increasing the equivalent spring rate to k/2. Fromthe point 204 to 205, two of the brake elements are activated, therebyincreasing the equivalent spring rate further to k. Theforce-displacement plots for the latter two ranges of motion are alsoshown in the plot of FIG. 21. As can be seen, the assembly of threeelements 210 allows the user to approximate a curve of arbitrary shape.Obviously, by using more elements 210 and also adding elements, andutilizing both serial (FIG. 20 a) and parallel (FIG. 20 b)configurations, almost any force (moment or torque) versus displacement(rotation) curve could be achieved.

It will be appreciated by those skilled in the art that for propersequence of brake element activation and deactivation, sensory devicescan be employed to measure the relative displacement of the joint (theconnected objects). In addition, since the walk-assist devices, forexample the aforementioned one attached to the ankle joint, must undergomore than one back and forth motion during each cycle of stride (seeFIG. 7), and as a result, at one ankle joint angle several instantaneousspring rates and instantaneous joint moments have to be present,therefore a control unit, preferably based on a programmablemicroprocessor, is needed to provide the proper sequence of brakeelement activation and deactivation (and potential energy release ifrequired).

It is also noted that in most cases, at the end of each stride cycle, abalance of potential energy may be present in one or more of the springelements of the walk-assist device. This was not the case for theaforementioned isolated walk-assist device used on a subject ankle sincethe amount of energy absorbed by the leg muscles acting on the anklejoint was shown to be smaller than the amount of energy that the legmuscles have to provide to increase the potential and/or kinetic energyof the leg. Since some of the joints are like the former and some likethe latter, a whole leg or body mounted walk-assist device needs to linkthe joints, preferably by passive mechanisms or at most by mechanismsequipped with brake (clutch) elements, and utilize a control system(preferably operated by a programmable microprocessor) to sequentiallyactivate and deactivate the brake (clutch) elements to tend to balancethe aforementioned energy requirements at each joint.

In addition, a walk-assist device that is equipped with a microprocessorcontrol can use sensory information from the joint angles (such aspotentiometer or optical encoder type of sensors) to optimally time theaforementioned sequence of activation and deactivation of the brake andclutch elements as, for example, the subject changes the pace ofwalking, or is walking on an inclined (up or down) surface, etc. Inanother embodiment, at least one accelerometer (e.g., a MEMS basedtri-axial type accelerometer) is also used (mounted on the subject body,such as on the waist together with the programmable control unit) tofurther tune the aforementioned operation of the walk-assist device. Theoperation of the walk-assist device can be improved further by providingat least one gyro (such as a MEMS type) to measure changes in the bodyangle and use it in the determination of the optimal timing of theactivation and deactivation of the brake elements.

In one embodiment of this invention, the programmable microprocessor isused for the aforementioned purpose of timing brake element activationand deactivation to achieve proper force (moment or torque) versusdisplacement (rotation) characteristics for proper operation of thewalk-assist device as described above. The brake element activation anddeactivation timing is based on one or more of the aforementioned jointangle and/or body acceleration sensory information.

In another embodiment, the programmable microprocessor is used for theaforementioned purpose as well as for adapting to the variations in thewalking pattern, walking up and down stairs, walking up or down aninclined surface, etc.

In another embodiment, the programmable microprocessor is used for oneor both of the aforementioned purposes as well as allowing the user toadjust the control parameters and the brake element activation anddeactivation sequencing to increase or decrease the effectiveness of thewalk-assist device in reducing the amount of work that is done by themuscles during walking or running in order to allow the muscles to getcertain amount of exercise.

The role of the aforementioned programmable microprocessor and thecontrol unit in other embodiments is described below.

In an alternative embodiment, manual or automatic gearing and/or cammechanisms, similar to a gear on a bicycle, is used instead ofprogrammable microprocessor based control unit to adjust the pattern andlevel of forces (moments and torque) generated by the passive elementsso as to provide the desired level of assist and match it to thechanging pattern of walking or running, such as moving up or down asloped surface or stairs.

In FIGS. 19 b and 19 c, the elements 210 and 211 are shown to have afinite, even though preferably small, size. However, the elements 210and 211 are preferably very small and a relatively large number of themused in the construction of walk-assist devices, and as such act asquasi-distributed brake and clutch systems. Such quasi-distributed brakeand clutch systems could be constructed using active materials such aspiezoelectric films and fibers and magnetorheological fluids.

In the above embodiments, power activated brake elements such as theelement 197 is used to engage or disengage the walk-assist device byisolating the spring elements of the system such as shown in FIG. 20 b.In FIG. 20 b, 191 and 192 are the aforementioned components that areconnected to the walk-assist device to allow deformation of the springelement 195 during its operation. By positioning the brake element 197in series with the spring element 195, the spring element 195 can beisolated by deactivating (disengaging) the brake element 197.

In the embodiment shown in FIG. 20 b, however, a power operatedengagement/disengagement clutch is used for the aforementioned purposeinstead of brake element 197, partly to minimize electrical powerconsumption. In general, whenever possible, engagement/disengagementclutches are preferable to braking elements. However, when smoothtransition from the engaged to the disengaged states is desired, brakeelements are preferable since the applied braking force can beregulated. In addition, braking elements can also be used to limit thetransmitted force unlike clutches with positive engagement/disengagementmechanisms.

In the embodiment shown in FIG. 20 b, the brake element is replaced witha manually operated engagement/disengagement clutch, which are wellknown in the art. This is particularly suitable for walk-assist deviceswith partly or wholly passive elements.

In the above embodiments, spring elements are directly and withoutintermediate mechanisms to store mechanical energy to be absorbed by thewalk-assist device and return it in the same manner to the leg system.The mechanical energy may, however, be directed to the spring elementvia a certain mechanism, such as a ratchet type of mechanism for thepurpose of storing energy during several cycles of gate and releasing itat a desired portion of the stride, or once a desired level of potentialenergy is stored in the spring, or as programmed in the microprocessorcontrol unit. The higher levels of potential energy may be required toincrease the efficiency of the device receiving the released potentialenergy, such as the efficiency of a boot integrated cooling device.

In this section of the disclosure, the present method and relateddevices are described as applied to one joint of the lower extremity,across two or more joints, or across all the joints of the lowerextremity. It is readily seen by those skilled in the art that theproposed walk-assist devices can be designed to cover both lowerextremity and interconnected to provide added stance stability andtransfer energy from one leg to the other to further reduce the“locomotion energy” and the “stance energy”. Such walk-assist devicescan be equipped with the aforementioned active elements and theiroperation is controlled by programmable microprocessors.

Methods and Devices to Generate Electrical Energy While Reducing Fatigue

Various devices have been made to allow a human to generate usefulelectrical power. The most common such device is the bicycle dynamo thatis brought into contact with the tire to generate electrical energy topower lights and certain other electrical and electronic devices.Dynamos rotated by hands through a handle have been used for variouspurposes including for powering fielded communication devices. In recentyears, attempt has also been made to generate electrical energy duringwalking, for example by incorporating piezoelectric elements directly orthrough other mechanical devices in the sole of the shoes to utilizepressure exerted by the weight of the subject to deform an elasticelement or pressurize certain fluid and use the stored potential and/orkinetic energy to generate electrical energy.

However, in all the methods considered to date for generating electricalenergy by a human subject, the subject has to spend energy to producethe mechanical energy that is used by the energy conversion device orsystem. As a result, the subject becomes tired, particularly if powerhas to be generated over a considerable amount of time. In addition, dueto the inherent inefficiency of all energy conversion systems, thesubject has to spend a significantly higher amount of energy than isproduced by the energy conversion system. This is the primary reason whysuch power generation methods and developed devices have not foundwidespread usage, except for extremely low power levels such as very lowpower implanted sensors and devices, and for emergency situations.

In this disclosure, methods are presented for generating electricalpower by a human subject while participating in a variety of activitiessuch as walking or running. The primary difference between the disclosedmethods and all other currently available methods is that with themethods disclosed herein, a subject can generate electrical power whilewalking or running, while at the same time reducing his/her fatigue byreducing the aforementioned “locomotion energy”. In other words, asubject using a power generating device based on the disclosed methodscan generate electrical energy while walking or running, while at thesame time saving energy, i.e., getting less tired than he/she would havebecome if he/she were not wearing the device.

The electrical energy generating devices constructed based on thedisclosed method can be attached to one or more of the joints of thelower extremities. These devices would preferably be similar to lowprofile braces worn on the knee, ankle or the hip joints. The size ofeach device is related to the amount of available mechanical energy atthe joint and the amount of electrical power that needs to be produced.For example, for low power requirements, the device may closely resemblean elastic joint support, that is worn under the garment. The preferablejoints for such devices are the knee joint for low power requirementsand the ankle joint for higher power requirements. This is generally thecase since for the knee joint, the device could be built as a knee pad,and for the ankle joint, the device could be built into a boot (orshoe). For maximum electrical power generation, the aforementionedwalk-assist mechanisms that interconnect all the lower extremity jointscan be used. The mechanical to electrical energy conversion may utilizepiezoelectric polymers or fibers, coil and magnet, or any other similarenergy conversion components.

In the following segment of this disclosure, the present methods aredescribed by their application to an electrical energy generation devicefor a human ankle joint, which allows the user to generate electricalenergy during walking while at the same time getting less tired.However, the method is general, and can be used similarly to constructdevices for other joints, such as the knee or hip joints or to be usedwith the aforementioned walk-assist devices that interconnect all thelower extremity joints. The method also applies to other periodic linearand/or rotational motion of other segments of the body during walking orrunning. For such periodic linear and/or rotational motions, devicesthat operate in a manner similar to those for the lower extremity jointscan be constructed to generate electrical energy while reducing theamount of mechanical energy that the related muscles have to provide.

For the ankle joint, the plots of FIGS. 4, 7 and 8 were shown toindicate that the muscles acting at the ankle joint have to do work toabsorb potential and/or kinetic energy of the leg in the range A to B,FIGS. 4 and 7, corresponding to the range P6 to P9 along Arrow 120 inFIG. 8, of the stride. The muscles acting at the ankle joint also workto increase the potential and/or kinetic energy of the leg in the rangeB to C, FIG. 4, corresponding to the range P9 to P15, FIG. 8, of thestride. It was shown that the area under the joint angle versus jointmoment curve from point P6 to point P9 and the zero moment (M_(A)) lineis the aforementioned work (referred to as W_(ab)) that the leg muscleshave to do to absorb the kinetic and/or potential energy of the legduring the corresponding portion of the stride. The area under the abovecurve from point P9 to point P15 and the zero moment (M_(A)) line is theaforementioned work (referred to as W_(add)) that the leg muscles haveto do to add kinetic and/or potential energy to the leg system duringthe corresponding portion of the stride.

Similar intervals were also shown for the knee joint in FIG. 2 d. As canbe seen in FIG. 2 d, there are three intervals, labeled as N1, N2, N3and N4, within which the input power is negative. During theseintervals, the leg muscles, as a whole, are absorbing energy and theknee torque (moment), FIG. 2 c, and angular velocity, FIG. 2 b, are inopposing directions.

The net mechanical work done by the muscles acting on the knee joint toabsorb the energy during each of the N1, N2 and N3 intervals isdetermined by equation (2) for the time interval t₁ to t₂, t₃ to t₄ andt₅ to t₆, respectively, and are given in Table 1. The internal N4 isrelatively small and is not included in Table 1. As can be seen in Table1, the right leg muscles absorb a total of approximately 250 mJ ofenergy during each stride. The amount of energy absorbed by the legmuscles acting on the ankle joint can be similarly determined. TABLE 1Work Done to Absorb Power at the Knee Interval Time interval Work (mJ)N1 t₁-t₂ 55.4 N2 t₃-t₄ 85.1 N3 t₅-t₆ 110

From the data presented in Table 1, the walking subject is seen to needto spend 250 mJ of energy in the time interval t₁ to t₂, t₃ to t₄ and t₅to t₆ by the muscles acting on the knee joint to sustain gate. Thisenergy is spent for the purpose of absorbing kinetic and potentialenergy of the leg. The electrical energy generation method beingdisclosed is based on providing external means to absorb this energyrather than requiring the subject to spend energy via the leg muscles.

In one embodiment, such an external device is attached to the leg at theknee joint, and transforms the aforementioned mechanical energy intoelectrical energy using an appropriate mechanical to electrical energyconversion system such as a magnet and coil or an appropriatepiezoelectric based mechanism.

In a similar manner, the kinetic and/or energy to be absorbed by themuscles acting at the ankle joint during the portion of the stride frompoint A to point B, FIG. 4 (corresponding to the range P6 to P9 alongthe arrow 120 in FIG. 8), can be transformed into electrical energyusing a similar external electrical power generating device.

When the energy to be absorbed by the leg muscles is absorbed by anexternal means such as the disclosed electrical power generating system,the walking subject has to spend less energy and is thereby lessfatigued during walking.

In general, one may not want to convert all the available mechanicalenergy to electrical energy. The remaining mechanical energy is thenstored in the aforementioned “locomotion energy” reducing devices toreduce the required locomotion energy as previously described. Thus, themethods and devices disclosed here can reduce fatigue as wells asgenerate electrical energy. This is particularly useful in light of thefact that the amount of electrical energy that is generally needed byhandheld electronics devices is much less than the total mechanicalenergy to be absorbed by the leg muscles during walking. Therefore inmost situations, only a portion of the aforementioned mechanical energyneeds to be converted to electrical energy. Secondly, partial conversionof the available mechanical energy to electrical energy can be achievedusing a very simple conversion system as described below. Lastly, theunused portion of the available mechanical energy is not wasted but usedto reduce the locomotion energy as was previously described.

It is noted that walk-assist devices may be constructed with only theenergy absorbing components. Such devices would only reduce or eliminatethe need for the muscles to work to absorb the aforementioned kineticand/or potential energy of the leg during walking and running. In otherwords, such walk-assist devices, unlike the aforementioned “locomotionenergy” reducing walk-assist devices, do not store and return theabsorbed mechanical energy to the limbs. The absorbed energy is,however, available for other uses, e.g., for generating electricalenergy as previously described. For this reason, hereinafter, thismethod of constructing walk-assist devices is referred to as the “energydissipative” method. A number of embodiments of such walk-assist devicesare provided below.

In one embodiment of such a device, the mechanical energy-absorbingelement is an electrical energy generator.

In another embodiment of such a device, the mechanical energy-absorbingelement transforms the mechanical energy into heat using, for example, abraking device.

In yet another embodiment of such a device, the mechanicalenergy-absorbing element transforms the mechanical energy into anotherform of mechanical energy such as potential energy of a pressurizedfluid or kinetic energy of a flywheel. The pressurized fluid may then beused to run a micro-turbine to generate electrical energy or the like.The kinetic energy stored in the flywheel may also be used for similarpurposes.

In yet another embodiment of such a device, the mechanicalenergy-absorbing element transfers the energy directly to another energyconsuming system such as a personal cooling system. In one embodiment,the entire system is integrated into the subject's boots. In anotherembodiment, the head, and/or the upper body are cooled with thedisclosed system. When the source of cooling is positioned relativelyfar from the intended cooling region, for example if the cooling systemis integrated into the boots and the head is intended to be cooled, thenit may be more efficient to convert the mechanical energy first toelectrical energy and then use electrical energy to cool the head usingsolid state cooling or the like. In yet another embodiment, drinkingfluid or food is cooled by the system.

In yet another embodiment of such a device, the mechanicalenergy-absorbing element transfers the energy directly to another energyconsuming system such as a personal heating system, particularly forwarming the most vulnerable limbs such as feet and toes, hands, etc.

In yet another embodiment of such a device, the mechanicalenergy-absorbing element is a combination of two or more of theaforementioned elements. In one embodiment of such a device, a control(switching) unit is provided to either regulate the amount of energytransferred to each element, e.g., to keep the body at certaintemperature. The control unit is preferably operated by a programmablemicroprocessor.

The above embodiments provide walk-assist devices that besides providingthe intended benefits, for example heating or cooling the body, theywould also reduce the user fatigue by reducing the amount of muscle workthat the user has to perform.

Similar to the aforementioned embodiments for power generation, one maynot want to transfer all the available mechanical energy to the aboveelements (brake, cooling, heating, etc. elements). In which case, theremaining mechanical energy is then stored in the aforementioned“locomotion energy” reducing devices and used to reduce the requiredlocomotion energy as previously described.

The aforementioned power generating walk-assist embodiments is describedfirst for a walk-assist device mounted at the ankle joint similar tothat of FIG. 9. The links 133 and 134 are still joined by the rotaryjoint 135 and are fixed to the leg cuff 132 and the foot piece (shoe)131, respectively. In FIG. 22, the links 133 and 134 are shown alone.The links 133 and 134 are provided by structural means for attaching thepower generating elements, in this case by stems 220 and 221,respectively. In an embodiment, an elastic element 223 (band, strip,spring, etc.) is used to connect the stems 220 and 221. At some pointalong the element 223, an electric power-generating device 224, theoperation of which is described later in this disclosure, is mounted.The characteristics of the elastic element 223 and its free length areselected according to the aforementioned procedure described for the“locomotion energy” reducing walk-assist devices. The length of theelastic element allows it to become loose (no tension) at the link 133position 222 and onward as the link 133 is rotated clockwise, therebyproviding no resistance to the ankle joint rotation (this range startsfrom around the point P6 to P5, continuing to point P15, as shown inFIG. 8). However, starting from the point P6, the elastic element 223becomes taut (shown in broken line), and as the link 133 is rotatedcounterclockwise, the elastic element provides a moment about the anklejoint, which would in the best possible situation, follow the anklejoint angle versus moment curve shown in FIG. 8 from the point P6 allthe way or part of the way to the point P9 in the direction 122.

In one embodiment of this invention, the power-generating element 224 isconstructed using piezoelectric materials. One such piezoelectricmaterial based power-generating element 224 (hereinafter, referred to asthe piezo generator) is shown in the schematics of FIGS. 23 a and 23 b.In FIG. 23 a, the piezo generator 224 is attached to the elastic element223 with a parallel configuration by the attachment means 225, which canbe made out of the same elastic material as elastic element 223. In FIG.23b, the piezo generator 224 is attached in series to the elasticelement 223. In general, the effective spring rate of the piezogenerator 224 is desired to be close to that of the elastic element 223to maximize the amount of mechanical energy to be converted toelectrical energy by the piezo generator 224. It is noted that byapplying tensile or compressive stress to a piezoelectric element, acharge is generated that could then be harvested by well knownelectronics circuits and stored in capacitors or used to chargerechargeable batteries. During each cycle of stride, the mechanicalenergy that is not converted to electrical energy is returned to the legsystem to reduce the work of the muscles while they need to increase thekinetic and/or potential energy of the leg system.

The piezo generator may be a stacked type; a thin film type with aflexible backing; fiber type, particularly of the type that are formedto significantly increase allowable elongation; made as a stack 230 ofbending beams as shown in FIG. 24 a, with each beam covered by a sheetof piezoelectric material; or any other numerous configurations that areknown in the art. In general, the piezoelectric elements must beprevented from being subjected to a considerable amount of tensile forcesince they are fairly brittle and could easily be fractured. This can bedone by the design of the piezo generator or by preloading said elementsin compression to a level that with the applied tensile force theelement still remains under compressive loading.

The piezo generator embodiment 230 shown schematically in FIG. 24 a isdesigned to subject piezoelectric elements (preferably in thin strips)to compressive loading achieved through bending. Each piezo generator230 is constructed with basic bending elements 236 and 237 shown inFIGS. 24 b and 24 c, respectively. Each element 236 and 237 consists ofa relatively long bending beam 231, over which a strip of piezoelectricmaterial is bonded using preferably a thin layer of relatively stiffepoxy or other similar bonding agent. In one embodiment, the bondingmaterial is conducting and forms one of the electrodes of thepiezoelectric strip element as described below. Each of the beamelements 231 are provided with steps 233 that extend above the surfaceof the piezoelectric strips 232. The difference between the two bendingelements 236 and 237 is the position of the step, for the element 236the step 233 is on the left side and for the element 237 the step 233 ison the right side, FIGS. 24 b and 24 c, respectively. The two elements236 and 237 are preferably symmetrical so that one would only need to berotated to form the other. The elements 236 and 237 are then stacked,one on the top of the other, to form the basic assembly of the piezogenerator 230, FIG. 24 a. The stacks are attached by attaching one step233 to the appropriate surface of the other beam as shown in FIG. 24 a.The steps may be attached to the beams by fasteners, adhesive bonding,or any other available method known in the art. In one embodiment, thestep and the beam are attached by sliding one into a provided guide(e.g., a dove tail or square shaped type- not shown in FIGS. 24 a-24 c),which are preferably locked by an appropriate bonding material such asepoxy. In another embodiment, the beams and steps are constructed from asingle strip of beam material, preferably aluminum. The piezoelectricstrips 232 are first bonded at appropriate positions and then bendedinto the form of the piezo generator 230. The steps 233 may also beeliminated to simplify the parts and the bending process. However,noting that one of the functions of the steps in 230 is to make the endsof the deflecting beams more rigid, thereby maximizing the amount of thebending of the beams in areas that are covered by the piezoelectricstrips. This function may, however, be provided in the case of a stripof beam material with uniform thickness (without the step 233 ), forexample, by making the bent areas wider, thereby stiffer.

During walking, as the elastic element 223, FIG. 22, is stretched, thepiezo generator is stretched, and a pair of forces 235 are applied tothe piezo generator 230, subjecting the beams 231 to bending, therebysubjecting the outer layer of the beam, i.e., the piezoelectric strip tocompressive stress. The piezoelectric strips would thereby produce avoltage and charge, which can then be harvested as described below. Theschematic of the piezo generator under the applied pair of tensileforces 235 (provided by the elastic elements 223, 225 ) is shown in FIG.25. In general, the piezoelectric strip is preferably preloaded incompression to avoid subjecting it to tensile forces. To make theattachment of the piezo generator to the elastic elements 223 or 225 orany other element, relatively rigid end pieces 234 can be provided.

Under the applied pair of tensile forces 235, the beam elements 231 bendas shown in FIG. 25, thereby allowing the total length of the piezogenerator 230 to increase. The total amount of work done by the force235 over the elongation of the piezo generator length is equal to themaximum amount of energy that is ideally available to be harvested.However, a considerable portion of the available mechanical energy isstored in the beam elements and other structural elements of the piezogenerator 230 and the piezoelectric strips as strain energy, and is notavailable as electrical charge for harvesting as electrical energy. Forthe case of the beams and connecting structures of the piezo generator230, the aforementioned strain is due to the deformation pattern of thewhole structure as a spring. The piezoelectric strips, as deformed, actas part of the structure of the piezo generator 230 to resist theapplied load. The deformation of the piezo generators would also induceinternal charges that tend to increase the resistance of thepiezoelectric strips to the aforementioned deformation, thereby makingthem effectively stiffer. The amount of work that the applied forces 235have performed to overcome the aforementioned internal resistance of thepiezoelectric strips is the amount of energy available for harvesting.In general, the rule of thumb is that when an external force deforms apiezoelectric element, about one-third of the work done by the externalforces is stored as electric potential in the piezoelectric element,i.e., about one-third of the input mechanical energy could be harvestedas electrical energy. Using the same rule of thumb, during each cycle ofstride, less than one-third of available mechanical energy stored in thepiezo generator 230 is available for conversion into electrical energy.It can therefore be observed that in the ideal situation, the beam andconnecting structures of the piezo generator 230 are desired to provideminimal resistance to deformation as a result of the applied forces 235,thereby transferring maximum mechanical energy to the piezoelectricelements.

The agent bonding the piezoelectric strips 232 to the beams 231 ispreferably very thin and has stiffness similar to that of the beam 231and has low damping so that the strain on the beam surface isefficiently transmitted to the piezoelectric strip 232. Thepiezoelectric strip is preferably poled such that as a result ofcompressive stress along the length of the strip, charge is produced onthe two surfaces of the strip, where the conducting electrodes arepositioned. In one embodiment, the bonding agent is conductive, andthereby makes the beam structure as the conducting medium connecting oneof the electrodes of a bank of piezoelectric strip elements together inparallel, this method of wiring such electrical power generators providerelatively high voltage output. Conductive bonding agents such as epoxyare commonly used in practice. The electric power generator and itselectrical energy collection and regulation electronics can then beconfigured as is common practice in the art, such as shown in theschematic of FIG. 26. In FIG. 26, each piezoelectric element is shownschematically as a capacitor 240, neglecting other smaller effects suchas resistance, etc. The capacitors are shown to be connected in series,even though they could be wired in series or partly in parallel and inseries in various configurations, depending on the number ofpiezoelectric elements and their capacitance in each particular case,and depending on the electrical energy collection and regulation element241 and the storage device 242, which could be capacitive, arechargeable battery or their combination. Alternatively, the electricalenergy collection and regulation element 241 may direct all or part ofthe collected electrical energy to some terminal electrical orelectronics loads (not shown) such as lighting, communications devices,heating elements, etc.

It is noted that piezoelectric elements may be constructed in a varietyof configurations, a number of which could be used to design piezogenerators similar to the element 230, in particular when the objectiveis not to maximize electrical power generation of the walk-assistdevice. It general, however, it is noted that to maximize the amount ofthe electrical energy that could be generated, the piezoelectricelements can provide nearly the same amount to the stiffness of thepiezo generator 230. Similarly, the piezo generator 224 can providenearly the same amount to the equivalent spring rate of the assembliesshown in FIGS. 23 a and 23 b as the elastic element 223.

In the assemblies of FIGS. 23 a and 23 b, an elastic element 223 isassembled in parallel or in series with a piezo generator 224.Alternatively, at least one piezo generator such as element 224, may beconfigured with at least one element 210 and/or at least one element211, FIGS. 19 b and 19 c, with or without other elastic (spring)elements, for use in place of the elements 223 and 224 in a walk-assistdevice provided at one joint of the subject, FIG. 22, or in theaforementioned assemblies connecting more than one lower extremity ofthe subject. The most appropriate configuration is dependent on eachspecific application. In a manner similar to that described for the“locomotion energy” reducing embodiments, a control unit equipped with aprogrammable microprocessor may be used to determine the sequence ofactivate and deactivate of the brake elements during walking. Theprogrammable microprocessor also allows the user to vary the parametersof the control algorithm such as the rate of electrical power generationor turn it off completely. Some of the major related embodiments aredisclosed below. However, it is appreciated by those skilled in the artthat numerous other combinations are possible, each of which couldprovide slightly or significantly different characteristics.

In one embodiment, the elastic element 223 and piezo generator 224element assembly shown in FIG. 23 a is modified with a brake element 211positioned in series with the piezo generator 224 as shown in FIG. 27,and indicated as element 250. As a result, by activating the brakeelement 211, the generator is placed in parallel with the elasticelement 223, and the assembly 250 operates as previously described forthe schematic of FIG. 23 a, i.e., as a power generating walk-assistdevice that reduces the required “locomotion energy”. However, bydeactivating the brake element 211, no power is generated and the devicebecomes a pure walk-assist device for reducing the “locomotion energy”.

In another embodiment 251 shown in FIG. 28, the brake element 211 ispositioned in series with a power generator 243. When the brake element211 is activated, the power generator 243 is operated and generateselectrical power. Otherwise the power generator 243 is deactivated. Inwalk-assist devices with passive elements only, manualengagement/disengagement clutches, a number of which are known in theart, can be used. Alternatively, power operated engagement/disengagementclutches, a number of which are known in the art, may be used instead ofthe brake element 211. The power generator 243 can be a dynamo typesince if properly selected, it would allow the walk-assist device tooperate at various speeds and its output can readily be controlled bythe system programmable microprocessor to provide optimal resistanceduring walking and or running.

In yet another embodiment, another of the aforementioned devices, suchas heating and or cooling elements are used in place of the powergenerator 243, FIG. 28, the operation of which could be controlled asdescribed above with the system programmable microcomputer.

In the embodiments of the disclosed electrical power generatingwalk-assist devices that are used on isolated lower extremity jointssuch as the ankle or the knee joints, the device can be readilyincorporated into wearable units already used widely for other purposes.For example, the electrical power generating walk-assist device used atthe ankle joint is readily incorporated into the boots being worn by thesubject. Or the electrical power generating walk-assist device for theknee joint can be constructed as a flexible knee bracing that, whichstrapped to the thigh and leg sides of the knee, which could also serveas a kneepad. In most of these cases, the mechanical to electricalenergy conversion component of the electrical energy generator ispreferably constructed with piezoelectric polymers or fibers to reducecomplexity, weight and volume and make it resistant to impact loading.

All the aforementioned embodiments may be constructed to be adjustable,both in physical size so as to match different subject geometries andalso in their operating characteristics, e.g., the level of power to beproduced during walking or the amount of walk assistance it shouldprovide. Such devices may be designed with a very specific task in mind,for example a knee brace type device might be designed for a hiker witha built-in GPS system. Or a device could be designed to power an MP3player, while a person is roller-blading, etc.

Methods and Devices for Selective Exercising of Muscles

The aforementioned “locomotion energy” reducing walk-assist methods andrelated devices are based on storing the mechanical energy to beabsorbed by the leg muscles as mechanical energy in elements such assprings, and providing it to the leg system when the leg muscles need towork to increase the kinetic and/or potential energy of the leg system.As a result, the total energy that the leg muscles have to spend duringwalking is reduced.

Now consider the situation in which the disclosed walk-assist device forreducing the “locomotion energy” is modified so that it would absorbenergy while the leg muscles are doing work to increase the kineticand/or potential energy of the leg system and that it inputs energy intothe leg system while the leg muscles are required to absorb energy. Thesubject using the resulting device must then spend more energy to walkthen they would without the device. As a result, the previouslywalk-assist device is turned into an exercise device and willhereinafter be referred to as an “exercise device” or a “muscle exercisedevice”.

In a manner similar to the disclosed “locomotion energy” reducingdevices, the “exercise devices” may be constructed for individual jointsor for more than one joint, including as a mechanism worn on both legs,including the hip joints. By wearing the “exercise device” on oneparticular joint and by selectively activating it during certainintervals of the joint(s) motions, one or a group of muscles arerequired to increase their work during walking and/or running, therebyturning the device into a selective “muscle exercise device” tostrengthen a particular set of muscles or simply for aerobic purposes.

In one embodiment, the device is designed to absorb energy only whilethe leg muscles are doing work to increase the kinetic and/or potentialenergy of the leg system. The energy to be absorbed can be transferredto any number of elements, including those described in the electricalpower generating walk-assist devices. For example, the energy to beabsorbed is transformed into heat using braking or damping elements, orused to generate electrical energy, or used to run a cooling system,etc.

In another embodiment, the disclosed walk-assist device for reducing the“locomotion energy” is modified and a mechanical energy storage devicesuch as a spring is used to absorb energy in the form of potentialenergy during the interval of the stride that the leg muscles are doingwork to increase the kinetic and/or potential energy of the leg system.Then during the interval of the stride that the leg muscles are used toabsorb mechanical energy to reduce kinetic and/or potential energy ofthe leg system, the potential energy stored in the aforementionedmechanical energy storage device is transferred to the leg system.

In yet another embodiment, the above two embodiments are combined suchthat energy is absorbed by transferring it partly to one of theaforementioned mechanical energy using devices such as electrical powergenerators and is partly stored as potential energy and transferred tothe leg system while the leg muscles are working to absorb kineticand/or potential energy from the leg system.

In yet another embodiment, energy may be absorbed during walking byproviding energy absorbing elements in the shoes or boots (e.g., shoesole or bottom surface utilizing bending deformation) to get exercisesimilar to walking and/or running on sand. The device can have means toadjust the rate of energy absorption. Such energy absorbing meansinclude viscous or other friction elements used to generate heat, orother devices known in the art for heating or cooling the feet and/orsome other segments of the body.

All embodiments of this invention can be equipped with programmablemicroprocessors that can be used by the user to activate or deactivatethe exercising device; to select a particular muscle or a muscle groupfor exercise; and to increase or decrease the level of severity of theexercise. In devices equipped with mechanical energy absorbing elementsthat provide certain output, e.g., generate electrical energy or provideheating or cooling functions, such programmable microprocessor can beused to adjust their parameters. In another embodiment, manuallyoperated engagement/disengagement clutches or other similar elements areused to activate or deactivate the exercising devices; select aparticular muscle or a muscle group for exercise; or to adjust the levelof exercise.

The methods and devices used to exercise selected muscles or musclegroups is described mainly with their application to the lower extremityjoints, in particular the ankle joint. The disclosed methods are,however, general and applicable to the other joints of the body, bothindividually and as a group. The method also applies to other linearand/or rotational motion of other segments of the body that undergonearly periodic motion during walking or running.

Another embodiment illustrates how a walk-assist device for the anklejoint is modified into an exercise device. Consider the walk-assistdevice shown schematically in FIG. 9. In FIG. 29, the links 133 and 134are shown alone. The links 133 and 134 are provided by structural means252 and 253 for attaching a mechanical energy consuming element, in thiscase the assembly 251, FIG. 28. During walking, in the entire range ofankle joint motion except in the range corresponding to the ankle jointmoment versus ankle joint angle curve from the point P9 to the pint P15(during which time the muscles acting at the ankle joint are doing workto increase the kinetic and/or potential energy of the leg system), thebrake element 211 is deactivated. In part or the entire range of anklemotion from the point P9 to the point P15, the brake element 211 isactivated. As a result, during this phase of the stride, i.e., while themuscles are working about the ankle joint to increase the kinetic and/orpotential energy of the leg system, the muscles have to work even harderto overcome the resistance of the mechanical energy consuming element,in this case the electrical power generator 243. Alternatively, othermechanical energy consuming elements such as cooling, heat generatingelements such as viscous dampers or slipping brakes, etc., may bepositioned together or instead of the electrical power generatingelement 243. The aforementioned programmable microprocessor control unitis preferably used to activate and deactivate the brake element 211,preferably based on a signal from an ankle joint sensor. Theprogrammable microprocessor preferably allows the user to adjust thelevel of energy that is consumed by the mechanical energy consumingelement by either varying the brake element 211 activation anddeactivation timing, or by adjusting the parameters of the mechanicalenergy consuming element. The braking element 211 may be replaced by anengagement/disengagement clutch.

Such an embodiment is similar to the disclosed walk-assist device forreducing the “locomotion energy”, such as those shown schematically inFIGS. 9 or 13 for the ankle joint, except for the reversed action of theelastic mechanical (potential) energy storage elements. In thisembodiment, the elastic elements are selected and positioned such thatduring the interval of the stride that the muscles are doing work toincrease the kinetic and/or potential energy of the leg system, energyis also being transferred to the present device elastic element(s) aspotential energy. And during the interval of the stride that the musclesare working to absorb the kinetic and/or potential energy of the legsystem, the potential energy stored in the elastic element(s) of thedevice is returned to the leg system. As a result, during both of theabove intervals of the stride, the leg muscles have to work harder toalso supply potential energy to the elastic element(s) of the device,and later absorb the same potential energy.

Another embodiment is a combination of the above two embodiments. Forthe ankle joint alone, such a device is very similar to the embodimentshown in the schematic of FIG. 29, except that in place of the element251, either one of the elements shown in FIGS. 23 a, 23 b or 27 orelements with similar characteristics is used. The objective here is toreturn part of the available energy to the leg and transfer theremainder to a mechanical energy consuming element such as an electricalenergy generating element.

Methods and Devices to Reduce “Stance Energy”

During locomotion, the weight of the subject body and the load thathe/she is carrying (gravity generated loads) and the dynamics forces dueto the inertia of the body and the load are supported partly by themuscle forces and partly by the resisting forces, moments (torques)across these joints, which are provided mostly by the passive componentsof the joints such as ligaments and other connective tissues and thecontact forces between the condyles.

The motion across the joints of the lower extremities maybe divided intotwo basic groups. The first group consists of the joint rotations withminimal connective tissue resistance except for minimal friction forces,such as the knee joint rotation 109 and the ankle rotation 121, FIG. 3.These joint rotations are hereinafter called the “unconstrained jointrotations”. The remaining joint rotations and displacements (e.g., axialand shearing) are constrained, to various degrees, by the resistance ofthe connective tissues such as ligaments and the contact forces betweenthe affected condyles. These joint rotations and displacements arehereinafter called the “constrained joint rotations” and “constrainedjoint displacements”, respectively.

During walking, the required shearing, compressive and tensile forcesacross the “constrained joints”, i.e., the forces required to stabilizethe aforementioned “constrained joint displacements”, and the requiredmoments and torques about the “constrained joints”, i.e., moments andtorques required to stabilize the aforementioned “constrained jointrotations”, are provided mostly by the ligaments and other passiveconnective tissues and the contact forces between the joint condyles.The ligaments and other connective tissues and the contact forcesbetween the condyles provide the required resisting (stabilizing)forces, moments and torques across the “constrained joints” in responseto the components of the aforementioned static or dynamic forces andmoment and torques across these joints.

In normal conditions, the muscles generally contribute less to theaforementioned resistive or stabilizing forces, moments and torques.This is particularly the case when the forces generated by the musclesexpanding across a joint do not provide a significant component in thedirection of a “constrained joint displacement” or moment or torqueabout a “constrained joint rotation”. The muscles, however, are used toprovide additional moments to provide a margin of stability to theaforementioned “unconstrained joint rotations”, and to a varying degreeto the “constrained joint displacements” and “constrained jointrotations”. Stabilizing moments about the “unconstrained joints” arealso required to overcome static or nearly static forces during standingor during very slow walking such as walking with walkers, or whileperforming certain tasks while standing in place or moving very slowly,or the like. In general, while a subject uses his/her muscles to applystabilizing moments across the unconstrained joints, the subject usuallyalso applies stabilizing forces, moments and torques across the“constrained joints”. Hereinafter, the work done by the muscles toprovide the aforementioned stabilizing forces across both theunconstrained and the constrained joints of the lower extremities iscalled the “stance energy”.

In the “locomotion energy” reducing embodiments, the disclosed“walk-assist” devices provide the means to reduce the required work ofthe muscles in providing moment about the aforementioned “unconstrainedjoints” during walking. The objective is to introduce methods andrelated devices for “walk-assist” or “stance-assist” devices that can beused to reduce the aforementioned “stance energy” during walking orduring slow movements or standing still upright.

In general, the aforementioned “locomotion energy” reducing embodimentsalso help to reduce the “stance energy” in the following manner. Thework that the muscles have to perform to increase the kinetic and/orpotential energy during certain portions of the stride and then absorbthe kinetic and/or potential energy during certain other portions of thestride include the work needed to support the weight of the body.Therefore the “locomotion energy” reducing embodiments also reducecertain amount of “stance energy” that the muscles have to provide. Inaddition, the potential energy storage elements, e.g., the elastic orspring elements, used in all “locomotion energy” reducing embodimentswould resist a certain amount of rotation at the “unconstrained joints”,thereby increasing stance stability and reducing the need for muscles toprovide this portion of stabilizing moments about the “unconstrainedjoints”. Here, only those embodiments are considered that do not useclutch and/or brake elements to isolate the above elastic and springelements from the joint when the subject is not walking or running.

The basic method being disclosed for reducing “stance energy” is basedon providing stabilizing moments about the “unconstrained joints” to atleast support the weight of the subject, and preferably also supportsthe weight of the load that is being carried by the subject. In general,depending on the circumstances facing the subject, it might be desirableto provide more stabilizing moments than the required minimum to createa certain amount of stability margin. Similarly, it is sometimesdesirable to provide certain amount of added stabilizing forces and/ormoments and/or torques to the “constrained joints” of the subject. Ingeneral, all the above stabilizing forces, moments and torques arepreferably nonlinear functions of their respective displacements androtations, providing at least the minimum amount of stabilizing force,moment and torque about the preferred positioning of the joint, andincreasing with an accelerated rate with deviation from such preferredpositioning of the joint. This nonlinear characteristic of thestabilizing joint forces (moments and toques) are described in moredetail in the remaining portion of this disclosure.

In general, the aforementioned “locomotion energy” reducing walk assistdevices do also reduce the “stance energy” by a certain amount dependingon their moment versus joint angle characteristics of the springelements used to store and release potential energy during locomotion.With “locomotion energy” reducing walk-assist devices, a subject reduces“stance energy” during walking and running as well as while standingstill or walking very slowly. This is the case since during walking, thespring element supports at least part of the subject weight and providesadditional force, moment and torque across the “constrained joints”.While standing still, the spring elements resist joint rotation to someextent as the “unconstrained joints” rotate away from the position atwhich, or range(s) of positions within which, the spring elements aredesigned not to provide resisting moments.

The above discussion applies to all the disclosed walk-assistembodiments for reducing “locomotion energy” that are constructedprimarily with passive elements. For those embodiments that areconstructed with braking (clutch) elements, including those that areoperated by microprocessor-controlled, walk-assist devices thatsignificantly reduce both the “locomotion energy” and the “stanceenergy”, including “stance energy” during very slow walking or evenwhile standing still, and that ensures stance stability with anappropriate amount of stability margin can be constructed as isdescribed later in this section.

In one embodiment of the above walk-assist devices constructed withpassive elements, the springs are designed to produce nonlinear moment(torque) τ versus angular rotation θ characteristic similar to thatshown in FIG. 30. The moment (torque) shown in FIG. 30 is in addition tothe moment (torque) that in the previous section of this disclosure wasshown to be required by the walk-assist embodiments for reducing“locomotion energy” and/or for utilizing the energy to be absorbed bythe muscles to generate electrical energy or for some other purposes.The purpose of the added joint moment (torque) is to provide or increasestance stability during walking and running and/or as standing still orwalking very slowly. As can be seen in FIG. 30, in certain range ofjoint rotation Δ, the added moment (torque) could be zero, but beyondthat range (in one or both directions of rotation), the added moment(torque) is shown to increase with an accelerated rate. At relativelylarge angular rotations of the joint, the added moment (torque) becomesrelatively large, thereby effectively stopping any further jointrotation in that direction. Such “maximum” allowable joint rotations maybe manually adjustable.

In another embodiment, the “maximum” allowable joint rotation, the nomoment (torque) range Δ, and even the shape of the curve are madeadjustable utilizing the aforementioned brakes (clutches) and springelement assemblies, such as those shown in FIGS. 18-20 or disclosedpreviously. The adjustments may be done manually. A microprocessorcontroller with sensory inputs however, can also control theadjustments. Such sensory inputs could be accelerometers and/or gyrosattached to the subject body or sensors measuring joint angles and theirrates to predict an outset of stance instability.

In a variation of the above embodiment, the microprocessor control ofthe walk-assist device, particularly one that acts on all three jointsof the leg, provides adjustments to the resisting moment (torque) at the“unconstrained joints” to provide support for the weight of the subjectand to load being carried by the subject. The adjustment is preferablywith input from a total weight-measuring sensor, such as one provided inthe shoes or the boots. The subject using such a device can then carry alarger load while being assisted by the present walk-assist deviceduring walking or running.

In yet another embodiment of the present invention, the aforementionedsensory input are used to predict outset of stance instability and makeappropriate adjustment to the resisting joint moment (torque) to preventthe subject from suddenly falling or collapsing. In general, thestability is provided by an increase in the resisting joint moments(torques), eventually locking them in place to support the subjectweight in a highly stable and comfortable posture. As such, thewalk-assist device acts also as an emergency stance stability controldevice as well. Once the subject is in fill control of the situation,he/she or someone assisting the subject would operate the microprocessorcontrol with input(s) to allow the subject to regain full mobility, orbe helped to sit or lay down, etc., by varying the resisting moment(torque) acting on the “unconstraint joints”.

In all the above embodiments, the microprocessor control may be used toautomatically adapt the walk-assist device to provide stance stabilityor increase in response to an input from one or more of theaforementioned sensors or sensors measuring parameters indicatingfatigue, such as pulse rate, blood oxygen, EKG or the like. Themicroprocessor controller can be programmable to run various stored orinput programs.

Methods and Devices for Rehabilitation

Almost all the walk-assist devices described in the previous sectionscan be readily turned into rehabilitation devices designed to performone or more of the following tasks:

-   -   1. Reduce one or more of the “constrained joint” forces, moments        or torque to reduce connective tissue and/or contact forces.    -   2. Reduce forces applied to one or a group of specific ligaments        or other connective tissues.    -   3. Reduce condular contact forces, partially or entirely, at a        lower extremity joint.    -   4. Reduce forces transmitted by one or a group of muscles acting        across one or more of the lower extremity joints.    -   5. Reduce certain force, moment or torque that is transmitted        across a limb, e.g., the leg or the thigh.    -   6. Provide the means to adjust the above joint, connective        tissue, muscles and limb force, moment and torque.

The primary objective of the disclosed method and related devices is toaffect forces, moments and torques that are transmitted across the lowerextremity joints and/or limbs or their various components withoutsignificantly affecting the subject locomotion capabilities. This isgenerally done for therapeutic and/or rehabilitative purposes, or toallow locomotion in the presence of injury to one or more of the above,or following certain surgical procedures or the like. For this reason,it is highly desirable that the aforementioned reduction or increase inthe joint, limb, connective tissue, muscle, etc., be adjustable. In thissection of the disclosure, the present method is described by itsapplication to one of the embodiments of the present invention.

In the most effective embodiment, an aforementioned walk-assist forreducing “locomotion energy” and “stance energy” with several activeelements such as units 210 and 211 and with microprocessor control ismodified as follows to provide the desired rehabilitative or therapeuticeffect. The embodiment is described as employed on a single joint of thelower extremity. The disclosed embodiment can similarly be applied todevices covering two or more of the lower extremity joints.

In one embodiment, several spring and (brake) clutch elements and unitssimilar to 210 and 211 are connected in parallel and/or in series aspreviously described and their actions are controlled by amicroprocessor. The primary function of the microprocessor control unitis to activate and deactivate the brake and clutch elements so that theranges of motion in which the device absorbs or provides energy to theleg system are selected such that the amount of force that a certainmuscle or a group of muscles must apply (and tendons must bear) and/orthe reaction forces at the condular surfaces of the joint, jointligaments or other connective tissues. The method of reducing muscleforces during locomotion and stance was described above. The condularcontact over the entire surface of the joint or a portion of it (e.g.,on the lateral or the medial side) is generally reduced by allowing thewalk-assist device to provide spring-generated loads on the appropriateside of the joint. For example, if condular contact on the lateral sideof the knee joint is to be reduced, the walk-assist device providesappropriate amounts of spring force during each range of the jointmotion. The condular contact forces may be similarly increased. The loadacross the joint ligaments and other soft tissues are similarlycontrolled.

In certain situations, the preloading of the spring elements of theabove embodiment may have to be initially adjusted to allow thewalk-assist device to provide the appropriate force levels during theentire cycle of the gate.

The rehabilitation devices disclosed herein can be controlled by aprogrammable microprocessor to achieve a prescribed pattern of muscle,tendon, ligament and condular forces. The force levels can then bevaried over time to achieve the desired rehabilitative effects. Inparticular, such devices can be used for rehabilitation or for generalmuscle strengthening purposes. For example, such devices can be designedto allow a patient to reduce load on a specific joint or a muscle or agroup of muscles or ligaments, with the potential of enabling a patientwith injury to a hard and/or soft tissue to gain early mobility, andallow gradual increased loading of the injured members as they heal andas a means to enhance the healing process.

In an alternative embodiment, particularly if the walk-assist devicedoes not have to vary the above connective tissue, contact force ormuscle force patterns in a complex manner, for example if it only needto reduce the entire condular contact force or reduce the forcetransmitted through a specific ligament, then a walk-assist with onlypassive elements may suffice. In such walk-assist devices, the springloads and preloading and other parameters of the device are preferablyadjustable to match a wide range of adjustments.

Other Applications For the Disclosed Methods and Devices

The methods and devices disclosed in the previous sections can directlyand with minor modifications be applied to certain sports activities toenhance performance or for training. For example, the aforementioned“locomotion energy” reducing method and devices can directly be used toreduce the energy spent during bicycling. The only modification neededis the adaptation of the joint moment (torque) versus anglecharacteristics from those of walking (e.g., FIGS. 2 and 4-8) to thoseof bicycling. In many sports, for example, cycling, swimming, rowing andthe like, the disclosed “sport assist” devices are preferably passive.As it was shown previously in this disclosure, even totally passivedevices could cover at least a certain portion of the activity cycle,thereby making a significant improvement in performance.

In one embodiment, the “sport assist” devices are designed to increasethe performance of the user in bicycling.

In another embodiment, the “sport assist” devices are designed toincrease the performance of the user in rowing.

In yet another embodiment, the “sport assist” devices are designed toincrease the performance of the user in swimming.

In yet another embodiment, the “sport assist” devices are designed toincrease the performance of the user in swimming under water with fins.

In yet another embodiment, the “sport assist” devices are designed to beadjustable so that its performance could be readily matched to theindividual user.

In yet another embodiment, the “sport assist” devices are designed forexercising certain muscles and muscle groups important to a specificsport.

In addition, the walk-assist devices designed to reduce “locomotionenergy” and “stance energy” and which span both legs of the subject mayalso be used to minimize or even eliminate the need for the leg muscleto do work during normal walking. Such devices can be designed withstance stability and allow input energy by powered actuation devices orpreferably by the arms or muscles of the subject's upper body. In suchdevices, mechanical energy is readily transferred by the arms or upperbody muscles by simply extending or compressing one or more of thepotential energy storage springs of the walk-assist device. Theaforementioned active elements can then be used to direct the storedpotential energy to the required joints. The amount of mechanical energyneeded from the external sources, the arms or the upper body muscles isminimal during walking on a flat surface, since the disclosedwalk-assist devices for reducing “locomotion energy” and “stance energy”were shown to be capable of significantly reducing the need for work bythe leg muscles. Such walk-assist devices are preferably equipped withthe aforementioned active elements and their operation is controlled byprogrammable microprocessors to make them highly efficient. Suchwalk-assist devices will require a relatively small amount of inputenergy by the arms or the upper body muscles, and could be used by thosewho have minimal or even no use of their lower extremity muscles, andolder people as a replacement for walkers of different types. In suchapplications, the walk-assist device is preferably equipped with theaforementioned sensor activated stance stability braking devices.

While there has been shown and described what is considered to bepreferred embodiments of the invention, it will, of course, beunderstood that various modifications and changes in form or detailcould readily be made without departing from the spirit of theinvention. It is therefore intended that the invention be not limited tothe exact forms described and illustrated, but should be constructed tocover all modifications that may fall within the scope of the appendedclaims.

1. A method for reducing an exerted energy associated with musclesacting across a joint, the method comprising: storing energy during oneor more periods of a periodic motion of the joint in which energy isabsorbed by the muscles; and at least partially returning the storedenergy to the muscles during one or more periods of the periodic motionin which the muscles are performing work.
 2. The method of claim 1,wherein the joint is the ankle.
 3. The method of claim 1, wherein thejoint is the knee.
 4. The method of claim 1, wherein the periodic motionis walking.
 5. The method of claim 1, wherein the periodic motion isrunning.
 6. The method of claim 1, wherein the storing of energy is donein a mechanical device.
 7. The method of claim 1, further comprising:sensing variations in the periodic motion; and adjusting one or more ofthe energy stored and the energy returned based on the sensing.
 8. Themethod of claim 1, further comprising allowing a user to adjust one ormore of the energy stored and the energy returned.
 9. The method ofclaim 1, wherein the storing comprises storing energy from two or morecycles of the periodic motion and the at least partially returningcomprises returning the stored energy at a predetermined portion of theperiodic motion.
 10. A device for reducing an exerted energy associatedwith muscles acting across a joint, the device comprising: means forstoring energy during one or more periods of a periodic motion of thejoint in which energy is absorbed by the muscles; and means for at leastpartially returning the stored energy to the muscles during one or moreperiods of the periodic motion in which the muscles are performing work.11. The device of claim 10, wherein the joint is the ankle.
 12. Thedevice of claim 10, wherein the joint is the knee.
 13. The device ofclaim 10, wherein the periodic motion is walking.
 14. The device ofclaim 10, wherein the periodic motion is running.
 15. The device ofclaim 10, wherein at least one of the means for storing energy and themeans for at least partially returning the stored energy is passive. 16.The device of claim 10, wherein at least one of the means for storingenergy and the means for at least partially returning the stored energyis active.
 17. A device for reducing a locomotion energy associated withleg muscles acting across an ankle joint, the device comprising: a cuffworn on the leg; a shoe; and a mechanism operatively connecting the cuffand shoe for storing energy during one or more periods of a walking orrunning motion of the joint in which energy is absorbed by the musclesand at least partially returning the stored energy to the muscles duringone or more periods of the walking or running motion in which themuscles are performing work.
 18. The device of claim 17, wherein themechanism comprises: a first intermediate member attached to the shoe; asecond intermediate member attached to the cuff, the first and secondintermediate parts being rotatably connected at a hinge; and a springprovided at the hinge which engages the first and second intermediatemembers during the one or more periods of the walking or running motionof the joint in which energy is absorbed by the muscles and disengagesduring the one or more periods of the walking or running motion in whichthe muscles are performing work.
 19. The device of claim 18, wherein thespring is selected from a group consisting of a torsional spring, acompressive spring, and an elastic element.
 20. The device of claim 17,wherein the mechanism comprises: a member operatively connected at oneend to the cuff; and first and second elastic elements fixed at one endto the shoe and at another end to the member such that the first andsecond elastic elements are stretched during the one or more periods ofthe walking or running motion of the joint in which energy is absorbedby the muscles and are relaxed during the one or more periods of thewalking or running motion in which the muscles are performing work.